Experimental description: Results from two laboratory experiments will be presented. In both experiments, a two-layer sample consisting of a top layer of epoxy, representing the impervious cap rock, and a lower layer of Bentheimer sandstone (porosity ~ 22%, permeability 1.34 Darcy, density 2080 kg/m3), representing the reservoir rock, is used. In the first experiment, ultrasonic tests using piezoelectric transducers were performed under ambient (room) conditions of temperature and pressure, and water was displaced by ethanol. In the second experiment, elaborate ultrasonic experiments were carried out under controlled (elevated) pressure and temperature conditions mimicking a true CO2 reservoir where supercritical CO2 displaced brine. An array of seismic receiver was used to record the ultrasonic reflections from the top and the bottom of the porous layer.

Results and conclusions: Using non-physical (or ghost) reflections retrieved by seismic interferometry, we could successfully estimate the acoustic wave velocity in the porous reservoir and its temporal change associated with changes in pressure and fluid-content in the pores. The estimation of layer-specific wave-velocity, eliminating effectively the effect of the changes occurring in the overburden and that of source irreproducibility, has been possible for the first time. The advantage of using cross-coherence over cross-correlation in the application of seismic interferometry, in order to address velocity changes in a thin reservoir layer, has been established. It was possible to obtain reliable values of the rock-physical properties from the estimated layer-specific acoustic wave velocity obtained by the proposed approach.","ultrasonics; interferometry; monitoring; CO2; CCS; reflections; seismics","en","abstract","","","","","","","","","","","","","","" "uuid:9e6a58de-eacd-4b8d-b56a-c3778112f97e","http://resolver.tudelft.nl/uuid:9e6a58de-eacd-4b8d-b56a-c3778112f97e","Space-based aperture array for ultra-long wavelength radio astronomy","Rajan, R.T.; Boonstra, A.J.; Bentum, M.; Klein-Wolt, M.; Belien, F.; Arts, M.; Saks, N.; Van der Veen, A.J.","","2015","The past decade has seen the advent of various radio astronomy arrays, particularly for low-frequency observations below 100 MHz. These developments have been primarily driven by interesting and fundamental scientific questions, such as studying the dark ages and epoch of re-ionization, by detecting the highly red-shifted 21 cm line emission. However, Earth-based radio astronomy observations at frequencies below 30 MHz are severely restricted due to man-made interference, ionospheric distortion and almost complete non-transparency of the ionosphere below 10 MHz. Therefore, this narrow spectral band remains possibly the last unexplored frequency range in radio astronomy. A straightforward solution to study the universe at these frequencies is to deploy a space-based antenna array far away from Earths’ ionosphere. In the past, such space-based radio astronomy studies were principally limited by technology and computing resources, however current processing and communication trends indicate otherwise. Furthermore, successful space-based missions which mapped the sky in this frequency regime, such as the lunar orbiter RAE-2, were restricted by very poor spatial resolution. Recently concluded studies, such as DARIS (Disturbuted Aperture Array for Radio Astronomy In Space) have shown the ready feasibility of a 9 satellite constellation using off the shelf components. The aim of this article is to discuss the current trends and technologies towards the feasibility of a space-based aperture array for astronomical observations in the Ultra-Long Wavelength (ULW) regime of greater than 10 m i.e., below 30 MHz. We briefly present the achievable science cases, and discuss the system design for selected scenarios such as extra-galactic surveys. An extensive discussion is presented on various sub-systems of the potential satellite array, such as radio astronomical antenna design, the on-board signal processing, communication architectures and joint space-time estimation of the satellite network. In light of a scalable array and to avert single point of failure, we propose both centralized and distributed solutions for the ULW space-based array. We highlight the benefits of various deployment locations and summarize the technological challenges for future space-based radio arrays.","radio astronomy; ultra-long wavelength; interferometry; feasibility study; system design","en","journal article","Springer","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Microelectronics","","","","" "uuid:6debab43-6c38-48ce-acb7-55cbae48f654","http://resolver.tudelft.nl/uuid:6debab43-6c38-48ce-acb7-55cbae48f654","A method to retrieve an improved high resolution reflection response from HiCLIMB array recordings of local earthquake scattering coda (PPT)","Hartstra, I.E. (TU Delft Applied Geophysics and Petrophysics); Wapenaar, C.P.A. (TU Delft ImPhys/Acoustical Wavefield Imaging; TU Delft Applied Geophysics and Petrophysics)","","2015","We discuss a method to interferometrically retrieve the body wave reflection response from local high-frequency scattering coda wave fields with the purpose to obtain an input dataset suitable for the application of advanced exploration-type imaging methods","scattering coda; interferometry; scattering mean free path; reflection response; impedance contrasts; advanced exploration-type imaging; coda attenuation factor; HiCLIMB array","en","conference paper","","","","","","","","","","","","","","" "uuid:6d0ac8a1-3880-4df6-bfb4-d4b96563284a","http://resolver.tudelft.nl/uuid:6d0ac8a1-3880-4df6-bfb4-d4b96563284a","Creating virtual vertical radar profiles from surface reflection ground penetrating radar data","Slob, E.C.; Hunziker, J.W.; Thorbecke, J.W.; Wapenaar, C.P.A.","","2014","","virtual source; virtual receiver; interferometry; autofocusing; 3D GPR","en","conference paper","UCL , COST","","","","","","","","Civil Engineering and Geosciences","Geoscience & Engineering","","","","" "uuid:f4cbaf4e-7240-40d0-a274-681e775e4700","http://resolver.tudelft.nl/uuid:f4cbaf4e-7240-40d0-a274-681e775e4700","On the improvement of heterodyne displacement interferometry: Enhancing measurement linearity and system modularity","Meskers, A.J.H.","Munnig Schmidt, R.H. (promotor); Spronck, J.W. (promotor)","2014","Lithographic exposure equipment for integrated circuit manufacturing requires ever more accurate position measurement systems, which is currently led by the advent of Extreme UltraViolet (EUV)-lithography machines. This PhD-research describes an interferometric displacement measurement system that possess the potential to foresee in the need for measurement accuracy in lithography systems far into this century. Besides the demanding measurement accuracies in these machines, also the size extension of the silicon substrates from 300 mm to 450 mm presents a challenge. The progress of these aspects promotes the improvement or development of new measurement tools for lithographic exposure equipment. The aim of this research was to design a “compact heterodyne displacement interferometer for a measurement range of 450 mm that achieves sub-nm measurement uncertainty, while allowing for a modular system buildup that has a flexible optical layout and is robust enough for fast module replacement to reduce downtime”. When operating in a vacuum (or near-vacuum) environment, periodic nonlinearity (PNL) is the main factor that limits the measurement linearity of a heterodyne interferometer that is supplied by a coaxial optical beam. This research has reduced this error source by replacing the coaxial optical beam by two separated optical beams, which resulted in a decrease of PNL from 0.1 nm to 0.004 nm. This reduction eliminates the need for calibration and digital compensation and thereby enables displacement measurement of quasi-static measurement targets and measuring more real time (i.e. there is no need any more for digital PNL compensation) respectively, which was previously not possible with sub-nm accuracy. Furthermore, the implemented interferometer concept also enabled the used of optical fiber delivery instead of using free-space optical beams. The use of optical fibers ensures a flexible optical layout that is robust enough for fast interferometer module replacement and reduces downtime due to the plug-and-play nature of optical fibers. This research has additionally resulted in a new method for measurement of optical wavefronts and a new method for generating the split frequency that is required for heterodyne interferometry.","interferometry; fiber-optics; electro optics; periodic nonlinearity; EUV lithography; heterodyne interferometer","en","doctoral thesis","","","","","","","","","Mechanical, Maritime and Materials Engineering","Precision and Microsystems Engineering","","","","" "uuid:2e291ac6-fda9-4ce6-8440-ff70df147c7f","http://resolver.tudelft.nl/uuid:2e291ac6-fda9-4ce6-8440-ff70df147c7f","Validation of separated source frequency delivery for a fiber-coupled heterodyne displacement interferometer","Meskers, A.J.H.; Spronck, J.W.; Munnig Schmidt, R.H.","","2014","The use of optical fibers presents several advantages with respect to free-space optical transport regarding sourcefrequency delivery to individual heterodyne interferometers. Unfortunately, fiber delivery to individual coaxial heterodyne interferometers leads to an increase of (periodic) nonlinearity in the measurement, because transporting coaxial frequencies through one optical fiber leads to frequency mixing. Coaxial beams thus require delivery via free-space transportation methods. In contrast, the heterodyne interferometer concept discussed in this Letter is based on separated source frequencies, which allow for fiber delivery without additional nonlinearity. This investigation analyzes the influence of external disturbances acting on the two fibers during delivery, causing asymmetry in phase between the two fibers (first-order effect), and irradiance fluctuations (second-order effect). Experiments using electro-optic phase modulation and acousto-optic irradiance modulation confirmed that the interferometerconcept can measure with sub-nanometer uncertainty using fiber delivered source frequencies, enabling fully fiber-coupled heterodyne displacement interferometers.","instrumentation, measurement, and metrology; interferometry; metrology; optical design of instruments; optical systems; phase measurement","en","journal article","Optical Society of America","","","","","","","","Mechanical, Maritime and Materials Engineering","Precision and Microsystems Engineering","","","","" "uuid:4dab07ba-394d-456a-9bda-2632a45e5ed4","http://resolver.tudelft.nl/uuid:4dab07ba-394d-456a-9bda-2632a45e5ed4","On the Marchenko equation for multicomponent single-sided reflection data","Wapenaar, C.P.A.; Slob, E.C.","","2014","Recent work on the Marchenko equation has shown that the scalar 3-D Green’s function for a virtual source in the subsurface can be retrieved from the single-sided reflection response at the surface and an estimate of the direct arrival. Here, we discuss the first steps towards extending this result to multicomponent data. After introducing a unified multicomponent 3-D Green’s function representation, we analyse its 1-D version for elastodynamic waves in more detail. It follows that the main additional requirement is that the multicomponent direct arrival, needed to initiate the iterative solution of the Marchenko equation, includes the forward-scattered field. Under this and other conditions, the multicomponent Green’s function can be retrieved from single-sided reflection data, and this is demonstrated with a 1-D numerical example.","interferometry; controlled source seismology; wave scattering and diffraction","en","journal article","Oxford University Press","","","","","","","","Applied Sciences","ImPhys/Imaging Physics","","","","" "uuid:bd5deced-cefd-4c44-9df2-c1b4969bd4b0","http://resolver.tudelft.nl/uuid:bd5deced-cefd-4c44-9df2-c1b4969bd4b0","Heterodyne displacement interferometer, insensitive for input polarization","Meskers, A.J.H.; Spronck, J.W.; Munnig Schmidt, R.H.","","2014","Periodic nonlinearity (PNL) in displacement interferometers is a systematic error source that limits measurement accuracy. The PNL of coaxial heterodyne interferometers is highly influenced by the polarization state and orientation of the source frequencies. In this Letter, we investigate this error source and discuss two interferometer designs, designed at TU Delft, that showed very low levels of PNL when subjected to any polarization state and/or polarization orientation. In the experiments, quarter-wave plates (qwps) and half-wave plates (hwps) were used to manipulate the polarization state and polarization orientation, respectively. Results from a commercial coaxial system showed first-order PNL exceeding 10 nm (together with higher order PNL) when the system ceased operation at around ±15°??hwp rotation or ±20°??qwp rotation. The two “Delft interferometers,” however, continued operation beyond these maxima and obtained first-order PNLs in the order of several picometers, without showing higher order PNLs. The major advantage of these interferometers, beside their high linearity, is that they can be fully fiber coupled and thus allow for a modular system buildup.","instrumentation, measurement, and metrology; interferometry; metrology; optical design of instruments; optical systems; phase measurement","en","journal article","Optical Society of America","","","","","","","","Mechanical, Maritime and Materials Engineering","Precision and Microsystems Engineering","","","","" "uuid:f1750374-9a25-4f81-a5d5-e99279aec31e","http://resolver.tudelft.nl/uuid:f1750374-9a25-4f81-a5d5-e99279aec31e","Data-driven Green's function retrieval and application to imaging with multidimensional deconvolution","Broggini, F.; Wapenaar, C.P.A.; Van der Neut, J.R.; Snieder, R.","","2014","An iterative method is presented that allows one to retrieve the Green's function originating from a virtual source located inside a medium using reflection data measured only at the acquisition surface. In addition to the reflection response, an estimate of the travel times corresponding to the direct arrivals is required. However, no detailed information about the heterogeneities in the medium is needed. The iterative scheme generalizes the Marchenko equation for inverse scattering to the seismic reflection problem. To give insight in the mechanism of the iterative method, its steps for a simple layered medium are analyzed using physical arguments based on the stationary phase method. The retrieved Green's wavefield is shown to correctly contain the multiples due to the inhomogeneities present in the medium. Additionally, a variant of the iterative scheme enables decomposition of the retrieved wavefield into its downgoing and upgoing components. These wavefields then enable creation of a ghost-free image of the medium with either cross correlation or multidimensional deconvolution, presenting an advantage over standard prestack migration.","autofocusing; Marchenko; scattering; interferometry; Green's function","en","journal article","American Geophysical Union","","","","","","","2014-07-17","Civil Engineering and Geosciences","Geoscience & Engineering","","","","" "uuid:dcef2bbe-a323-434d-b5cc-aa7b5b7dd6e8","http://resolver.tudelft.nl/uuid:dcef2bbe-a323-434d-b5cc-aa7b5b7dd6e8","Nanostep height measurement via spatial mode projection","Hermosa, N.; Rosales-Guzman, C.; Pereira, S.F.; Torres, J.P.","","2014","We demonstrate an optical scheme for measuring the thickness of thin nanolayers with the use of light beam’s spatial modes. The novelty in our scheme is the projection of the beam reflected by the sample onto a properly tailored spatial mode. In the experiment described below, we are able to measure a step height smaller than 10 nm, i.e., one-eightieth (1/80) of the wavelength with a standard error in the picometer scale. Since our scheme enhances the signal-to-noise ratio, which effectively increases the sensitivity of detection, the extension of this technique to the detection of subnanometric layer thicknesses is feasible.","interferometry; height measurements; phase measurement; sensors; subwavelength structures; nanostructures","en","journal article","Optical Society of America","","","","","","","","Applied Sciences","ImPhys/Imaging Physics","","","","" "uuid:ae38d8e5-667c-4a4c-ace2-5ba6eae1aeb6","http://resolver.tudelft.nl/uuid:ae38d8e5-667c-4a4c-ace2-5ba6eae1aeb6","The magmatic system beneath Torfajökull volcano, Iceland, throughradar and seismic interferometric analysis","Esteves Martins, Joana E. (TU Delft Mathematical Geodesy and Positioning); Hooper, Andy (University of Leeds); Ruigrok, E.N. (TU Delft Applied Geophysics and Petrophysics); Draganov, D.S. (TU Delft Applied Geophysics and Petrophysics); Hanssen, R.F. (TU Delft Mathematical Geodesy and Positioning); White, Robert (University of Cambridge); Soosalu, Heidi (Tallinn University)","","2014","Torfajökull is the largest silicic volcanic centre in Iceland lying at the intersection of the rift zone (MidAtlantic Ridge) and the transform zone that connects to Reykjanes peninsula. It erupts infrequently,with only two eruptions in the last 1200 years, the latest of which was over 5 centuries ago. Yet, itsactive tectonic setting, persistent high and low frequency seismicity, deformation and geothermalactivity within its large caldera (18x12 km diameter) indicate the continued presence of a long-lasting magma chamber. Here we speculate on possible geometry, size and depth of the Torfajökullmagma chamber by using radar interferometry (InSAR) and seismic interferometry (SI).Using InSAR time series analysis we detect a surface subsidence pattern at rates of up to ~13 mm yr-1in the SW region of Torfajökull ́s caldera, on-going since at least 1993. The subsidence rate isconstant in time, and perhaps due to a cooling magma chamber. The data can be fit reasonably wellusing a model of a NE-SW oriented spheroidal body at ~5 km depth. As the deflating area correlatesspatially with the area of geothermal activity, deflation may also be the surface response due to anactive hydrothermal circulation.To gain more insight into the geometry of Torfajökull’s magmatic system and rock properties of thesubsurface, we apply ambient noise seismic interferometry (SI) by cross-correlation of ambient noise.With this technique we can detect velocity variations, which can correspond to the edges of dikes ormolten magma bodies. Our tomographic results give reliable results of velocity variations within adepth range of 2 km to 7.5 km. We find high velocity zones that we interpret as old dike intrusions.Low velocity anomalies (>5%), which usually indicate the presence of warmer material, are locatedon the southeast and southwest part of the volcano, outside the volcano caldera.Finally we compare both InSAR and SI results. The hypothesis of a magma chamber under thesubsidence area detected by InSAR does not seem to fit the tomographic results, as the expectededges of a magma body modelled by InSAR are not clearly identified by the SI results. If there is anestablished magma chamber within Torfajökull caldera this is likely to be bellow 7km depth.","InSAR; ambient noise tomography (ANT); volcano; interferometry; Torfajokull volcano","en","abstract","","","","","","","","","","","","","","" "uuid:e20ca783-dd51-4b40-a86b-e5750977f785","http://resolver.tudelft.nl/uuid:e20ca783-dd51-4b40-a86b-e5750977f785","Wavefront spacing and Gouy phase in presence of primary spherical aberration","Pang, X.; Fischer, D.G.; Visser, T.D.","","2013","We study the Gouy phase of a scalar wavefield that is focused by a lens suffering from primary spherical aberration. It is found that the Gouy phase has different behaviors at the two sides of the intensity maximum. This results in a systematic increase of the successive wavefront spacings around the diffraction focus. Since all lenses have some amount of spherical aberration, this observation has implications for optical calibration and metrology.","diffraction theory; interferometry; metrology; phase","en","journal article","Optical Society of America","","","","","","","","Electrical Engineering, Mathematics and Computer Science","","","","","" "uuid:ed7d7c16-4570-4c65-a898-aeda07de6b8c","http://resolver.tudelft.nl/uuid:ed7d7c16-4570-4c65-a898-aeda07de6b8c","Surface wave retrieval in layered media using seismic interferometry by multidimensional deconvolution","Van Dalen, K.N.; Wapenaar, C.P.A.; Halliday, D.F.","","2013","Virtual-source surface wave responses can be retrieved using the crosscorrelation (CC) of wavefields observed at two receivers. Higher mode surface waves cannot be properly retrieved when there is a lack of subsurface sources that excite these wavefields, as is often the case. In this paper, we present a multidimensional-deconvolution (MDD) scheme that is based on an approximate convolution theorem. The scheme introduces an additional processing step in which the CC result is deconvolved by a so-called point-spread tensor. The involved point-spread functions capture the imprint of the lack of subsurface sources and possible anelastic effects, and quantify the associated spatial and temporal smearing of the virtualsource components that leads to the poor surfacewave retrieval. The functions can be calculated from the same wavefields as used in the CC method. For a 2-D example that is representative of the envisaged applications, we show that the deconvolution partially corrects for the smearing. The retrieved virtual-source response only has some amplitude error in the ideal situation of having the depth of the required vertical array equal to the depth penetration of the surface waves. The error is due to ignored cross-mode terms in the approximate convolution theorem. Shorter arrays are also possible. In the limit case of only a single surface receiver, the retrieved virtual-source response is still more accurate than the CC result. The MDD scheme is valid for horizontally layered media that are laterally invariant, and includes exclusively multicomponent point-force responses (rather than their spatial derivatives) and multicomponent observations. The improved retrieval of multimode surface waves can facilitate dispersion analyses in shallow-subsurface inversion problems and monitoring, and surface wave removal algorithms.","interferometry; surface waves and free oscillations; interface waves","en","journal article","Oxford University Press","","","","","","","","Civil Engineering and Geosciences","Structural Engineering","","","","" "uuid:720350ab-c150-4573-9621-a82f5f27e35e","http://resolver.tudelft.nl/uuid:720350ab-c150-4573-9621-a82f5f27e35e","Monitoring changes in velocity and Q using non-physical arrivals in seismic interferometry","Draganov, D.S.; Ghose, R.; Heller, K.; Ruigrok, E.N.","","2012","Application of seismic interferometry to records from receivers at the Earth’s surface from sources in wells retrieves the reflection response measured at the receivers as if from virtual sources located also at the surface. When the wavefields experience intrinsic losses during propagation, non-physical arrivals (ghosts) would appear in the retrieved result. These ghosts appear due to waves that reflect inside a subsurface layer. Thus, a ghost contains information about the seismic properties of the specific layer. We show how such ghosts can be used to monitor layer-specific changes in the velocity and intrinsic losses in the subsurface. We show how to identify the ghosts using numerical-modelling results from a vertical well, and how to estimate the layer-specific velocity and quality-factor changes using numerical-modelling results from a horizontal well as well as ultrasonic S-wave laboratory data.","downholemethods; interferometry; controlled source seismology; bodywaves; seismic attenuation","en","journal article","Royal Astronomical Society","","","","","","","2013-07-31","Civil Engineering and Geosciences","Geoscience & Engineering","","","","" "uuid:b7d52df3-f801-4a19-a252-32d85bf419cb","http://resolver.tudelft.nl/uuid:b7d52df3-f801-4a19-a252-32d85bf419cb","Interferometric redatuming by sparse inversion","Van der Neut, J.; Herrmann, F.J.","","2012","Assuming that transmission responses are known between the surface and a particular depth level in the subsurface, seismic sources can be effectively mapped to this level by a process called interferometric redatuming. After redatuming, the obtained wavefields can be used for imaging below this particular depth level. Interferometric redatuming consists of two steps, namely (i) the decomposition of the observed wavefields into downgoing and upgoing constituents and (ii) a multidimensional deconvolution of the upgoing constituents with the downgoing constituents. While this method works in theory, sensitivity to noise and artefacts due to incomplete acquisition require a different formulation. In this letter, we demonstrate the benefits of formulating the two steps that undergird interferometric redatuming in terms of a transform-domain sparsity-promoting program. By exploiting compressibility of seismic wavefields in the curvelet domain, the method not only becomes robust with respect to noise but we are also able to remove certain artefacts while preserving the frequency content. Although we observe improvements when we promote sparsity in the redatumed data space, we expect better results when interferometric redatuming would be combined or integrated with least-squares migration with sparsity promotion in the image space.","inverse theory; interferometry; controlled source seismology","en","journal article","Royal Astronomical Society","","","","","","","2013-06-06","Civil Engineering and Geosciences","Geoscience & Engineering","","","","" "uuid:5704e053-2454-4f35-996b-c23475b17dcc","http://resolver.tudelft.nl/uuid:5704e053-2454-4f35-996b-c23475b17dcc","Marine Controlled-Source Electromagnetic Interferometry","Hunziker, J.W.","Slob, E.C. (promotor); Wapenaar, C.P.A. (promotor)","2012","In marine Controlled-Source Electromagnetics, a boat tows an electric source, whose signal is travelling on various paths to the receiver stations at the ocean bottom. Unfortunately, the signal does not only travel via the subsurface to the receivers, but also directly through the water and via the air-water interface. Signals travelling on the latter two travelpaths do not contain any information about the subsurface. On the contrary, they cover a possible response from a subsurface reservoir. Therefore, one aims to suppress the signal travelling along those paths. Interferometry by multidimensional deconvolution replaces the overburden by a homogeneous halfspace suppressing any interactions with the air-water interface. Furthermore, the direct field is removed and the source is redatumed to a receiver position. Since interferometry by multidimensional deconvolution is a data-driven method, no information about the ocean or the subsurface is needed, except the material parameters at the receiver level. This thesis investigates the benefits and limitations of interferometry by multidimensional deconvolution applied to marine Controlled-Source Electromagnetic data.","electromagnetics; hydrocarbon exploration; interferometry","en","doctoral thesis","","","","","","","","","Civil Engineering and Geosciences","Geoscience & Engineering","","","","" "uuid:da7ffc75-626d-4654-bb60-a447fc7d01bb","http://resolver.tudelft.nl/uuid:da7ffc75-626d-4654-bb60-a447fc7d01bb","Interferometric applications with a femtosecond frequency comb laser in complementary spaces","Zeitouny, M.G.","P Urbach, H. (promotor)","2011","In the recent years, precision measurement techniques in the field of optical science have improved with the advances in the phase stabilization of femtosecond lasers. Due to their unique properties, phase stabilized femtosecond lasers, also known as frequency comb lasers, are used as a versatile tools, not only for time and frequency metrology, but also in fundamental physics, high-precision spectroscopy, distance metrology and laser noise characterization. In this thesis we mainly focus on two fundamental applications that are encountered in optical metrology: In the first part, we present a study of the formation of correlation patterns in a dispersive unbalanced Michelson interferometer using a frequency comb laser as a source. This was intended for accurate distance measurement in dispersive media. In the second part, we focus on the precise determination of laser spectra where we demonstrate measurement of single frequency comb modes using a conventional Fourier transform spectrometer. This can be used for broadband molecular spectroscopy with high resolution. The study of correlation patterns is specifically intended for distance measurement in dispersive media. There are several ways to determine distances using optical means. With pulsed lasers, the measurement of the time of flight-of-pulses provides a good estimation on the pulse propagation distance within a non-ambiguity range that corresponds to the pulse-to-pulse distance or equivalently the laser cavity length. For precision measurements, interferometric techniques are used to provide accurate information on the distance between the source and the target. These interferometric techniques can be implemented in two different domains: (1) in the time domain where the interference signal or the correlation pattern (in case of pulsed lasers) is measured using a single detector. (2) In the frequency domain where a spectrometer is placed at the output of the interferometer to provide spectral interference patterns. Regardless of the measurement method, the acquired data require further analysis in order to get the final results. Moreover, placing the measurement system in a dispersive medium such as air adds more complexity to the analysis. In the first part of this thesis, we study the case of distance measurement using correlation patterns where we focus on the effects of dispersion on the measured data. We will mainly try to understand (1) how correlations are formed using the frequency comb laser as a source, (2) whether the definition of the group refractive index is sufficient to correct for the dispersion effects and (3) to understand how the shape of the correlation patterns vary with the propagation distance in the dispersive medium. Therefore, we study the formation of correlation patterns using a rigorous mathematical model where results will be compared to experimental measurements. We first show that the discrete spectrum of the frequency comb laser yield correlation patterns that are mathematically described by a discrete series. This series shows that the knowledge of the electric field of the optical pulses is unnecessary and only an accurate knowledge of the power spectral density of the laser source together with the refractive index of the dispersive medium are sufficient to provide an accurate model of the correlation patterns. Using the discrete model of correlation patterns we have carried out simulation work by considering various spectral shapes, environmental conditions and distances. As a result, we show that for accurate distance determination, precise knowledge of the position of the brightest fringe that is the fringe having maximum contrast, of the correlation pattern is required. In vacuum, the distance can be accurately determined using the repetition rate of the laser and the position of the brightest fringe. In the case of pulse propagation in a dispersive medium such as air, the position of the brightest fringe is influenced by the shape of the power spectral density and the environmental parameters. Only in the case of perfectly symmetric power spectral densities, one can use the group refractive index definition to correct for the dispersion effects. With perfectly symmetric spectra, correlations appear to broaden linearly where no distortion effects can be seen even if the phase refractive index variation is nonlinear. Distortion effects are only seen when the power spectral density of the laser source has an asymmetric distribution. Moreover, we have experimentally and numerically observed that after a certain delay distance in air, the envelope of the correlation pattern takes a particular structure which is the shape of the power spectral density of the laser source. The discrete model of correlation patterns has been shown to be accurate enough to reproduce the correlation patterns as compared to experimental data. From this model we were able to extract the absolute measured distance in air. However, the discrete model has failed to explain some physical effects such as the shift of the central fringe and the envelope shape convergence after a certain delay distance in the dispersive medium. To explain these results, we extend the discrete model to a continuous model of cross-correlation functions and use the Poisson summation formula. This allows us to show that even for a homogenous dispersive medium the position of the brightest fringe varies non-linearly for small delay distances and stabilizes for longer ones. The distance where non-linear effects are important is shown to be dependent on the properties of the dispersive media and the initial spectrum of the transmitted pulse. In case of very large delay distances the particular values of the frequencies that are present in the spectrum play an important role since only specific frequencies contribute to specific fringes in the cross-correlation. These specific frequencies will be addressed as stationary frequencies where the method of stationary phase is applied to the continuous model aiming to describe the correlation patterns in the asymptotic regime of large delay distances. In the second part of this work, a new experimental scheme has been built allowing the measurement of single frequency comb modes with sub-MHz resolution. This study is specifically intended for molecular spectroscopy with high resolution using a broadband light. Spectroscopy involves the determination of accurate spectral lines on a frequency scale. The experimental setup consists of a conventional Fourier transform spectrometer where the measuring arm of the Michelson interferometer has a scanning length of 10 m. Depending on the repetition rate of the frequency comb laser (typically 100 MHz to 1GHz ), many correlation patterns (4 to10) are captured within this large scanning length. By applying a Fourier transform on the measured train of correlations (or series of correlations) one can obtain the frequency comb mode resolved spectrum. We also provide a complete study on the analysis steps that are required to get the final spectrum such as, accurate sampling, apodization and phase correction. Results have been validated by measuring the absorption lines of molecular transitions using a sample cell. As time and frequency domains are complementary, we therefore entitle this thesis ""Interferometric applications with a femtosecond frequency comb laser in complementary spaces"".","interferometry; spectroscopy","en","doctoral thesis","","","","","","","","","Applied Sciences","Imaging Science & Technology","","","","" "uuid:ce6afd90-098f-4f30-9a50-41e811923719","http://resolver.tudelft.nl/uuid:ce6afd90-098f-4f30-9a50-41e811923719","Fiber-coupled displacement interferometry without periodic nonlinearity","Ellis, J.D.; Meskers, A.J.H.; Spronck, J.W.; Munnig Schmidt, R.H.","","2011","Displacement interferometry is widely used for accurately characterizing nanometer and subnanometer displacements in many applications. In many modern systems, fiber delivery is desired to limit optical alignment and remove heat sources from the system, but fiber delivery can exacerbate common interferometric measurement problems, such as periodic nonlinearity, and account for fiber-induced drift. In this Letter, we describe a novel, general Joo-type interferometer that inherently has an optical reference after any fiber delivery that eliminates fiber-induced drift. This interferometer demonstrated no detectable periodic nonlinearity in both free-space and fiber-delivered variants.","instrumentation, measurement and metrology; fringe analysis; interferometry; metrological instrumentation; optical design of instruments; optical systems","en","journal article","Optical Society of America","","","","","","","","Mechanical, Maritime and Materials Engineering","Precision and Microsystems Engineering","","","","" "uuid:e23dede0-cc57-464e-ad42-77b49a1bb6e1","http://resolver.tudelft.nl/uuid:e23dede0-cc57-464e-ad42-77b49a1bb6e1","Extraction of P-wave reflections from microseisms","Ruigrok, E.N.; Campman, X.; Wapenaar, K.","","2011","The last few years there has been a growing number of body-wave observations in noise records. In 1973 Vinnik conjectured that P-waves would even be the dominant wavemode, at epicentral distances of about 40 degrees and onwards from an oceanic source. At arrays far from offshore storms, surface waves induced by nearby storms would not mask the body-wave signal and hence primarily P-waves would be recorded. We measured at such an array in Egypt and indeed found a large proportion of P-waves. At the same time, a new methodology is under development to characterize the lithosphere below an array of receivers, without active sources or local earthquakes. Instead, transmitted waves are used which are caused by distant sources. These sources may either be transient or more stationary. With this new methodology, called seismic interferometry, reflection responses are extracted from the coda of transmissions. Combining the two developments it is clear that there is a large potential for obtaining reflection responses from low-frequency noise. A potential practical advantage of using noise instead of earthquake responses would be that an array only needs to be deployed for a few days or weeks instead of months, to gather enough illumination. We used a few days of continuous noise, recorded with an array in the Abu Gharadig basin, Egypt. We split up the record in three distinct frequency bands and in many small time windows. Using array techniques and taking advantage of all three-component recordings we could unravel the dominant wavemodes arriving in each time window and in each frequency band. The recorded wavemodes, and hence the noise sources, varied significantly per frequency band, and -to a lesser extent- per time window. Primarily P-waves were detected on the vertical component for two of the three frequency bands. For these frequency bands, we only selected the time windows with a favorable illumination. By subsequently applying seismic interferometry, we retrieved P-wave reflection responses and delineated reflectors in the crust, the Moho and possibly the Lehmann discontinuity.","body waves; interferometry; ambient noise; microseism; lithosphere","en","journal article","Elsevier","","","","","","","","Civil Engineering and Geosciences","Geotechnology","","","","" "uuid:f5a0d542-c224-474a-b568-f99c1426d008","http://resolver.tudelft.nl/uuid:f5a0d542-c224-474a-b568-f99c1426d008","Long distance measurement with femtosecond pulses using a dispersive interferometer","Cui, M.; Zeitouny, M.G.; Bhattacharya, N.; Van den Berg, S.A.; Urbach, H.P.","","2011","We experimentally demonstrate long distance measurements with a femtosecond frequency comb laser using dispersive interferometry. The distance is derived from the unwrapped spectral phase of the dispersed interferometer output and the repetition frequency of the laser. For an interferometer length of 50 m this approach has been compared to an independent phase counting laser interferometer. The obtained mutual agreement is better than 1.5 ?m (3×10?8), with a statistical averaging of less than 200 nm. Our experiments demonstrate that dispersive interferometry with a frequency comb laser is a powerful method for accurate and non-incremental measurement of long distances.","instrumentation, measurement and metrology; interferometry; ultrafast measurements","en","journal article","Optical Society of America","","","","","","","","Applied Sciences","QN/Quantum Nanoscience","","","","" "uuid:1008d5f6-0ae4-47ec-8109-921721014a14","http://resolver.tudelft.nl/uuid:1008d5f6-0ae4-47ec-8109-921721014a14","Time-frequency distribution of interferograms from a frequency comb in dispersive media","Zeitouny, M.G.; Cui, M.; Janssen, A.J.; Bhattacharya, N.; Van den Berg, S.A.; Urbach, H.P.","","2011","We investigate general properties of the interferograms from a frequency comb laser in a non-linear dispersive medium. The focus is on interferograms at large delay distances and in particular on their broadening, the fringe formation and shape. It is observed that at large delay distances the interferograms spread linearly and that its shape is determined by the source spectral profile. It is also shown that each intensity point of the interferogram is formed by the contribution of one dominant stationary frequency. This stationary frequency is seen to vary as a function of the path length difference even within the interferogram. We also show that the contributing stationary frequency remains constant if the evolution of a particular fringe is followed in the successive interferograms found periodically at different path length differences. This can be used to measure very large distances in dispersive media.","correlators; spectrum analysis; interferometry; chirping; ultrafast spectroscopy","en","journal article","Optical Society of America","","","","","","","","Applied Sciences","IST/Imaging Science and Technology","","","","" "uuid:c4772e2c-caae-4123-b4af-c462f23f3489","http://resolver.tudelft.nl/uuid:c4772e2c-caae-4123-b4af-c462f23f3489","Seismic interferometry using multidimensional deconvolution and crosscorrelation for crosswell seismic reflection data without borehole sources","Minato, S.; Matsuoka, T.; Tsuji, T.; Draganov, D.S.; Hunziker, J.W.; Wapenaar, C.P.A.","","2011","Crosswell reflection method is a high-resolution seismic imaging method that uses recordings between boreholes. The need for downhole sources is a restrictive factor in its application, for example, to time-lapse surveys. An alternative is to use surface sources in combination with seismic interferometry. Seismic interferometry (SI) could retrieve the reflection response at one of the boreholes as if from a source inside the other borehole. We investigate the applicability of SI for the retrieval of the reflection response between two boreholes using numerically modeled field data. We compare two SI approaches — crosscorrelation (CC) and multidimensional deconvolution (MDD). SI by MDD is less sensitive to underillumination from the source distribution, but requires inversion of the recordings at one of the receiver arrays from all the available sources. We find that the inversion problem is ill-posed, and propose to stabilize it using singular-value decomposition. The results show that the reflections from deep boundaries are retrieved very well using both the CC and MDD methods. Furthermore, the MDD results exhibit more realistic amplitudes than those from the CC method for downgoing reflections from shallow boundaries. We find that the results retrieved from the application of both methods to field data agree well with crosswell seismic-reflection data using borehole sources and with the logged P-wave velocity.","geophysical techniques; interferometry; seismic waves; seismology","en","journal article","Society of Exploration Geophysicists","","","","","","","","Civil Engineering and Geosciences","Geoscience & Engineering","","","","" "uuid:6759f1cf-1c63-47c7-b481-c36b289cd44a","http://resolver.tudelft.nl/uuid:6759f1cf-1c63-47c7-b481-c36b289cd44a","Optical metrology techniques for dimensional stability measurements","Ellis, Jonathan David","Munnig Schmidt, R.H. (promotor); Spronck, J.W. (promotor)","2010","This thesis work is optical metrology techniques to determine material stability. In addition to displacement interferometry, topics such as periodic nonlinearity, Fabry-Perot interferometry, refractometry, and laser stabilization are covered.","optical metrology; material stability; interferometry; laser stabilization","en","doctoral thesis","","","","","","","","","Mechanical, Maritime and Materials Engineering","Precision and Microsystems Engineering","","","","" "uuid:29c9b91a-b337-4f1a-9190-ad37092ae384","http://resolver.tudelft.nl/uuid:29c9b91a-b337-4f1a-9190-ad37092ae384","Systematic comparison of the use of annular and Zernike circle polynomials for annular wavefronts","Mahajan, V.N.; Aftab, M.","","2010","The theory of wavefront analysis of a noncircular wavefront is given and applied for a systematic comparison of the use of annular and Zernike circle polynomials for the analysis of an annular wavefront. It is shown that, unlike the annular coefficients, the circle coefficients generally change as the number of polynomials used in the expansion changes. Although the wavefront fit with a certain number of circle polynomials is identically the same as that with the corresponding annular polynomials, the piston circle coefficient does not represent the mean value of the aberration function, and the sum of the squares of the other coefficients does not yield its variance. The interferometer setting errors of tip, tilt, and defocus from a four-circle-polynomial expansion are the same as those from the annular-polynomial expansion. However, if these errors are obtained from, say, an 11-circle polynomial expansion, and are removed from the aberration function, wrong polishing will result by zeroing out the residual aberration function. If the common practice of defining the center of an interferogram and drawing a circle around it is followed, then the circle coefficients of a noncircular interferogram do not yield a correct representation of the aberration function. Moreover, in this case, some of the higher-order coefficients of aberrations that are nonexistent in the aberration function are also nonzero. Finally, the circle coefficients, however obtained, do not represent coefficients of the balanced aberrations for an annular pupil. The various results are illustrated analytically and numerically by considering an annular Seidel aberration function.","active or adaptive optics; wave-front sensing; interferometry; optical design and fabrication; aberrations (global)","en","journal article","Optical Society of America","","","","","","","","Applied Sciences","","","","","" "uuid:bffc466e-3073-47c0-a35d-32c6366ae2bf","http://resolver.tudelft.nl/uuid:bffc466e-3073-47c0-a35d-32c6366ae2bf","High-resolution lithospheric imaging with seismic interferometry","Ruigrok, E.N.; Campman, X.; Draganov, D.S.; Wapenaar, K.","","2010","In recent years, there has been an increase in the deployment of relatively dense arrays of seismic stations. The availability of spatially densely sampled global and regional seismic data has stimulated the adoption of industry-style imaging algorithms applied to converted- and scattered-wave energy from distant earthquakes, leading to relatively high-resolution images of the lower crust and upper mantle.We use seismic interferometry to extract reflection responses from the coda of transmitted energy from distant earthquakes. In theory, higher resolution images can be obtained when migrating reflections obtained with seismic interferometry rather than with conversions, traditionally used in lithospheric imaging methods. Moreover, reflection data allow the straightforward application of algorithms previously developed in exploration seismology. In particular, the availability of reflection data allows us to extract from it a velocity model using standard multichannel data-processing methods. However, the success of our approach relies mainly on a favourable distribution of earthquakes. In this paper, we investigate how the quality of the reflection response obtained with interferometry is influenced by the distribution of earthquakes and the complexity of the transmitted wavefields. Our analysis shows that a reasonable reflection response could be extracted if (1) the array is approximately aligned with an active zone of earthquakes, (2) different phase responses are used to gather adequate angular illumination of the array and (3) the illumination directions are properly accounted for during processing. We illustrate our analysis using a synthetic data set with similar illumination and source-side reverberation characteristics as field data recorded during the 2000–2001 Laramie broad-band experiment. Finally, we apply our method to the Laramie data, retrieving reflection data. We extract a 2-D velocity model from the reflections and use this model to migrate the data. On the final reflectivity image, we observe a discontinuity in the reflections. We interpret this discontinuity as the Cheyenne Belt, a suture zone between Archean and Proterozoic terranes.","seismology; interferometry; body waves; crustal structure","en","journal article","Wiley-Blackwell","","","","","","","","Civil Engineering and Geosciences","Geotechnology","","","","" "uuid:a7510463-5446-4a49-a8fc-81f44db1d984","http://resolver.tudelft.nl/uuid:a7510463-5446-4a49-a8fc-81f44db1d984","Tutorial on seismic interferometry: Part 1 — Basic principles and applications","Wapenaar, C.P.A.; Draganov, D.S.; Snieder, R.; Campman, X.; Verdel, A.","","2010","Seismic interferometry involves the crosscorrelation of responses at different receivers to obtain the Green's function between these receivers. For the simple situation of an impulsive plane wave propagating along the x-axis, the crosscorrelation of the responses at two receivers along the x-axis gives the Green's function of the direct wave between these receivers. When the source function of the plane wave is a transient (as in exploration seismology) or a noise signal (as in passive seismology), then the crosscorrelation gives the Green's function, convolved with the autocorrelation of the source function. Direct-wave interferometry also holds for 2D and 3D situations, assuming the receivers are surrounded by a uniform distribution of sources. In this case, the main contributions to the retrieved direct wave between the receivers come from sources in Fresnel zones around stationary points. The main application of direct-wave interferometry is theretrieval of seismic surface-wave responses from ambient noise and the subsequent tomographic determination of the surface-wave velocity distribution of the subsurface. Seismic interferometry is not restricted to retrieving direct waves between receivers. In a classic paper, Claerbout shows that the autocorrelation of the transmission response of a layered medium gives the plane-wave reflection response of that medium. This is essentially 1D reflected-wave interferometry. Similarly, the crosscorrelation of the transmission responses, observed at two receivers, of an arbitrary inhomogeneous medium gives the 3D reflection response of that medium. One of the main applications of reflected-wave interferometry is retrieving the seismic reflection response from ambient noise and imaging of the reflectors in the subsurface. A common aspect of direct- and reflected-wave interferometry is that virtual sources are created at positions where there are only receivers without requiring knowledge of the subsurface medium parameters or of the positions of the actual sources.","geophysical techniques; Green's function methods; interferometry; seismic waves; seismology","en","journal article","Society of Exploration Geophysicists","","","","","","","","Civil Engineering and Geosciences","Geoscience & Engineering","","","","" "uuid:07504f32-d9fb-46b9-8095-dcfa5b3e817b","http://resolver.tudelft.nl/uuid:07504f32-d9fb-46b9-8095-dcfa5b3e817b","Tutorial on seismic interferometry: Part 2 — Underlying theory and new advances","Wapenaar, C.P.A.; Slob, E.C.; Snieder, R.; Curtis, A.","","2010","In the 1990s, the method of time-reversed acoustics was developed. This method exploits the fact that the acoustic wave equation for a lossless medium is invariant for time reversal. When ultrasonic responses recorded by piezoelectric transducers are reversed in time and fed simultaneously as source signals to the transducers, they focus at the position of the original source, even when the medium is very complex. In seismic interferometry the time-reversed responses are not physically sent into the earth, but they are convolved with other measured responses. The effect is essentially the same: The time-reversed signals focus and create a virtual source which radiates waves into the medium that are subsequently recorded by receivers. A mathematical derivation, based on reciprocity theory, formalizes this principle: The crosscorrelation of responses at two receivers, integrated over differ-ent sources, gives the Green's function emitted by a virtual source at the position of one of the receivers and observed by the other receiver. This Green's function representation for seismic interferometry is based on the assumption that the medium is lossless and nonmoving. Recent developments, circumventing these assumptions, include interferometric representations for attenuating and/or moving media, as well as unified representations for waves and diffusion phenomena, bending waves, quantum mechanical scattering, potential fields, elastodynamic, electromagnetic, poroelastic, and electroseismic waves. Significant improvements in the quality of the retrieved Green's functions have been obtained with interferometry by deconvolution. A trace-by-trace deconvolution process compensates for complex source functions and the attenuation of the medium. Interferometry by multidimensional deconvolution also compensates for the effects of one-sided and/or irregular illumination.","deconvolution; geophysical techniques; Green's function methods; interferometry; seismic waves; seismology","en","journal article","Society of Exploration Geophysicists","","","","","","","","Civil Engineering and Geosciences","Geoscience & Engineering","","","","" "uuid:9bf7fc0a-55ba-4cd0-91dd-b51b2064b638","http://resolver.tudelft.nl/uuid:9bf7fc0a-55ba-4cd0-91dd-b51b2064b638","On seismic interferometry, the generalized optical theorem, and the scattering matrix of a point scatterer","Wapenaar, C.P.A.; Slob, E.C.; Snieder, R.","","2010","We have analyzed the far-field approximation of the Green's function representation for seismic interferometry. By writing each of the Green's functions involved in the correlation process as a superposition of a direct wave and a scattered wave, the Green's function representation is rewritten as a superposition of four terms. When the scattered waves are modeled with the Born approximation, it appears that a three-term approximation of the Green's function representation (omitting the term containing the crosscorrelation of the scattered waves) yields a nearly exact retrieval, whereas the full four-term expression leads to a significant nonphysical event. This is because the Born approximation does not conserve energy and therefore is an insufficient model to explain all aspects of seismic interferometry. We use the full four-term expression of the Green's function representation to derive the generalized optical theorem. Unlike other recent derivations, which use stationary phase analysis, our derivation uses reciprocity theory. From the generalized optical theorem, we derive the nonlinear scattering matrix of a point scatterer. This nonlinear model accounts for primary and multiple scattering at the point scatterer and conforms with well-established scattering theory of classical waves. The model is essential to explain fully the results of seismic interferometry, even when it is applied to the response of a single point scatterer. The nonlinear scattering matrix also has implications for modeling, inversion, and migration.","geophysical techniques; Green's function methods; interferometry; seismic waves; seismology","en","journal article","Society of Exploration Geophysicists","","","","","","","","Civil Engineering and Geosciences","Geoscience & Engineering","","","","" "uuid:99b47e3b-f180-49a3-907a-ad0e07c89635","http://resolver.tudelft.nl/uuid:99b47e3b-f180-49a3-907a-ad0e07c89635","Retrieving electric resistivity data from self-potential measurements by cross-correlation","Slob, E.C.; Snieder, R.; Revil, A.","","2010","We show that the two-point cross-correlation of self-potential field recordings is equal to the electric resistivity between the two points. This holds under the condition that spatially and temporally uncorrelated noise sources exist throughout the volume. These sources should have a known amplitude spectrum and their correlated strengths should be proportional to the dissipative medium property function. Natural fluctuations, such as thermal noise, may occur that satisfy the necessary conditions. When these fluctuations are random deviations from a state of thermal equilibrium, the fluctuation-dissipation theorem can be used to describe these sources. Other types of sources may exist, such as the ones creating the self-potential field through coupling with fluctuations in pressure, temperature and chemical potential gradients.","interferometry; potential fields","en","journal article","American Geophysical Union","","","","","","","","Civil Engineering and Geosciences","Geotechnology","","","","" "uuid:0b417f3a-506b-4d13-bde5-ce212e9933e7","http://resolver.tudelft.nl/uuid:0b417f3a-506b-4d13-bde5-ce212e9933e7","Balanced interferometric system for stability measurements","Ellis, J.D.; Joo, K.N.; Spronck, J.W.; Munnig Schmidt, R.H.","","2009","We describe two different, double-sided interferometer designs for measuring material stability. Both designs are balanced interferometers where the only optical path difference is the sample and the reference beams are located within the interferometer. One interferometer is a double-pass design, whereas the other is a single-pass system. Based on a tolerancing analysis, the single-pass system is less susceptible to initial component misalignment and motions during experiments. This single-pass interferometer was tested with an 86nm thin-film silver sample for both short-term repeatability and long-term stability. In 66 repeatability tests of 30 min each, the mean measured drift rate was less than 1pm=h rms. In two long-term tests (>9 h), the mean drift rate was less than 1:1pm=h, which shows good agreement between the short- and long-term measurements. In these experiments, the mean measured length change was 2nm rms.","instrumentation; measurement; metrology; interferometry","en","journal article","Optical Society of America","","","","","","","","Mechanical, Maritime and Materials Engineering","Precision and Microsystems Engineering","","","","" "uuid:ec6ff55d-ecff-4eed-a0df-a2097d7d1c73","http://resolver.tudelft.nl/uuid:ec6ff55d-ecff-4eed-a0df-a2097d7d1c73","Interferometry by deconvolution of multicomponent multioffset GPR data","Slob, E.C.","","2009","Interferometric techniques are now well known to retrieve data between two receivers by the cross correlation of the data recorded by these receivers. Cross-correlation methods for interferometry rely mostly on the assumption that the medium is loss free and that the sources are all around the receivers. A recently developed method introduced interferometry by deconvolution that is insensitive to loss mechanisms by principle and requires sources only on one side of the receivers. In this paper, we develop such method for ground-penetrating radar, illustrate the concept, and discuss implications for practical applications with numerical examples.","deconvolution; ground-penetrating radar (GPR) data; interferometry; multicomponent; multioffset","en","journal article","IEEE","","","","","","","","Civil Engineering and Geosciences","Applied Geophysics and Petrophysics","","","","" "uuid:e61260cf-3c26-4a96-a548-f0da20209e10","http://resolver.tudelft.nl/uuid:e61260cf-3c26-4a96-a548-f0da20209e10","Simple heterodyne laser interferometer with subnanometer periodic errors","Joo, K.N.; Ellis, J.D.; Spronck, J.W.; Van Kan, P.J.M.; Munnig Schmidt, R.H.","","2009","We describe a simple heterodyne laser interferometer that has subnanometer periodic errors and is applicable to industrial fields. Two spatially separated beams can reduce the periodic errors, and the use of a right-angle prism makes the optical configuration much simpler than previous interferometers. Moreover, the optical resolution can be enhanced by a factor of 2, because the phase change direction is opposite between reference and measurement signals. Experiments have demonstrated the periodic errors are less than 0.15 nm owing to the frequency mixing of the optical source. The improvements for reducing the frequency mixing of the optical system are also discussed.","interferometry; metrological instrumentation; metrology","en","journal article","Optical Society of America","","","","","","","","Mechanical, Maritime and Materials Engineering","Precision and Microsystems Engineering","","","","" "uuid:42ff2f29-f270-4c4b-9f95-8bbbdf7469ba","http://resolver.tudelft.nl/uuid:42ff2f29-f270-4c4b-9f95-8bbbdf7469ba","Evaluation of DEM-assisted SAR coregistration","Nitti, D.O.; Hanssen, R.F.; recife, A.; Bovenga, F.; Milillo, G.; Nutricato, R.","","2008","Image alignment is without doubt the most crucial step in SAR Interferometry. Interferogram formation requires images to be coregistered with an accuracy of better than 1/8 pixel to avoid significant loss of phase coherence. Conventional interferometric precise coregistration methods for full-resolution SAR data (Single-Look Complex imagery, or SLC) are based on the cross-correlation of the SLC data, either in the original complex form or as squared amplitudes. Offset vectors in slant range and azimuth directions are computed on a large number of windows, according to the estimated correlation peaks. Then, a two-dimensional polynomial of a certain degree is usually chosen as warp function and the polynomial parameters are estimated through LMS fit from the shifts measured on the image windows. In case of rough topography and long baselines, the polynomial approximation for the warp function becomes inaccurate, leading to local misregistrations. Moreover, these effects increase with the spatial resolution and then with the sampling frequency of the sensor, as first results on TerraSAR-X interferometry confirm. An improved, DEM-assisted image coregistration procedure can be adopted for providing higher-order prediction of the offset vectors. Instead of estimating the shifts on a limited number of patches and using a polynomial approximation for the transformation, this approach computes pixel by pixel the correspondence between master and slave by using the orbital data and a reference DEM. This study assesses the performance of this approach with respect to the standard procedure. In particular, both analytical relationships and simulations will evaluate the impact of the finite vertical accuracy of the DEM on the final coregistration precision for different radar postings and relative positions of satellites. The two approaches are compared by processing real data at different carrier frequencies and using the interferometric coherence as quality figure.","Synthetic Aperture Radar (SAR); interferometry; coregistration; Digital Evaluation Model (DEM)","en","conference paper","SPIE","","","","","","","","Aerospace Engineering","Mathematical Geodesy & Positioning","","","","" "uuid:33d9e1a0-bf35-4439-b96d-0d20c75acd5e","http://resolver.tudelft.nl/uuid:33d9e1a0-bf35-4439-b96d-0d20c75acd5e","Compensation and optimization of dispersion in nulling interferometry","Spronck, J.F.P.; Los, J.W.N.; Pereira, S.F.","","2008","The optical properties of materials are wavelength-dependent. This property, called dispersion, affects the performance of a wide-band nulling interferometer by inducing wavelength-dependent phase differences between the arms of the interferometer. In this paper, we analyze the influence of dispersion in nulling interferometers for exoplanet detection.","interferometry; nulling interferometry; dis[persion; astronomical optics; exoplanet detection","en","conference paper","SPIE","","","","","","","","Applied Sciences","Optics Research Group","","","","" "uuid:12fe697e-9ae2-44c7-bdc8-95bce2e783e8","http://resolver.tudelft.nl/uuid:12fe697e-9ae2-44c7-bdc8-95bce2e783e8","The role of amplitude, phase, polarization and their interconnection in nulling interferometry","Spronck, J.F.P.","Braat, J.J.M. (promotor)","2008","Nulling interferometry is a promising technique to directly detect Earth-like exoplanets. Unfortunately, it is extremely challenging to build a nulling interferometer and to meet the requirements needed for Earth-like planet detection. In this, thesis, we analyze the role of amplitude, phase and polarization in nulling interferometry and we use this information to design new types of nulling interferometers.","optics; interferometry; astronomical optics; exoplanet; nulling interferometry","en","doctoral thesis","","","","","","","","","Applied Sciences","","","","","" "uuid:631d8e12-8e7a-4f69-af10-0bf758864bb7","http://resolver.tudelft.nl/uuid:631d8e12-8e7a-4f69-af10-0bf758864bb7","Seismic and electromagnetic interferometry: Retrieval of the earth's reflection response using crosscorrelation","Draganov, D.","Wapenaar, C.P.A. (promotor)","2007","One of the goals of exploration geophysics is to obtain an image of the subsurface. In petroleum exploration and near-surface geophysics, this is best achieved using reflected waves. For this, a controlled seismic or electromagnetic source is placed at the surface, activated, and the wavefields that it creates are recorded at the surface after being reflected from subsurface structures. However, it is not always possible to use controlled sources at the surface. An alternative is to make use of seismic or electromagnetic interferometry. By crosscorrelating wavefields, which are recorded at two points at the surface and result from sources around the two points, the reflection response can be retrieve between these two points as if there were a controlled source at one of the points and a receiver at the other. This book shows derivations of different seismic and electromagnetic interferometry relations using as a starting point two-way and one-way reciprocity theorems of the time-correlation type. Using numerically modeled data, the retrieval of the reflection response is investigated from the crosscorrelation of recorded wavefields from subsurface transient and noise sources. This is performed for acoustic, elastic and electromagnetic waves. The ability of seismic interferometry to retrieve reflection responses in practical applications is demonstrated with two examples. The first example uses laboratory data from an inhomogeneous granite block, where transmission recordings are crosscorrelated resulting from separate P-wave and S-wave transient sources. The second example is with field data from a desert area, where transmission recordings are crosscorrelated resulting from seismic background-noise sources in the subsurface.","seismic; electromagnetic; interferometry; reflection; retrieval; reciprocity","en","doctoral thesis","","","","","","","","","Civil Engineering and Geosciences","","","","","" "uuid:e69b3d1b-dda2-4b6b-a6e5-12ddb013f1e7","http://resolver.tudelft.nl/uuid:e69b3d1b-dda2-4b6b-a6e5-12ddb013f1e7","Vectorial analysis of polarization issues in multi-axial nulling interferometers for exoplanet detection","Spronck, J.; Pereira, S.F.; Braat, J.J.M.","","2007","We show the theoretical limitations of a multi-axial nulling interferometer with respect to longitudinal polarization. We furthermore analyze the filtering capabilities of a single-mode fiber in this case.","interferometry; polarization; astronomical optics; nulling interferometry","en","conference paper","SPIE","","","","","","","","Applied Sciences","Optics Research Group","","","","" "uuid:31ceb9fc-c41b-4dd7-b6e3-d159da6aa1a9","http://resolver.tudelft.nl/uuid:31ceb9fc-c41b-4dd7-b6e3-d159da6aa1a9","Design of a polarization nulling interferometer for exoplanet detection","Spronck, J.; Vosteen, L.L.A.; Pereira, S.F.; Braat, J.J.M.","","2007","We present the design of a new testbed experiment to demonstrate nulling interferometry using polarization properties. This three-beam set-up is perfectly symmetric with respect to the number of reflections and transmissions and should therefore allow a high rejection ratio in a wide spectral band.","interferometry; nulling interferometry; polarization; astronomical optics; exoplanet detection","en","conference paper","SPIE","","","","","","","","Applied Sciences","Optics Research Group","","","","" "uuid:a89005f2-07e1-4c2e-b293-20ef631cf2ae","http://resolver.tudelft.nl/uuid:a89005f2-07e1-4c2e-b293-20ef631cf2ae","General representations for wavefield modeling and inversion in geophysics","Wapenaar, C.P.A.","","2007","Acoustic, electromagnetic, elastodynamic, poroelastic, and electroseismic waves are all governed by a unified matrix-vector wave equation. The matrices in this equation obey the same symmetry properties for each of these wave phenomena. This implies that the wave vectors for each of these phenomena obey the same reciprocity theorems. By substituting Green's matrices in these reciprocity theorems, unified wavefield representations are obtained. Analogous to the well-known acoustic wavefield representations, these unified representations find applications in geophysical modeling, migration, inversion, multiple elimination, and interferometry.","acoustic waves; seismic waves; vectors; matrix algebra; interferometry","en","journal article","Society of Exploration Geophysicists","","","","","","","","Civil Engineering and Geosciences","Geotechnology","","","","" "uuid:d16d5860-72e6-45e9-9f56-0cfcb41d86ce","http://resolver.tudelft.nl/uuid:d16d5860-72e6-45e9-9f56-0cfcb41d86ce","Retrieval of reflections from seismic background?noise measurements","Draganov, D.S.; Wapenaar, K.; Mulder, W.; Singer, J.; Verdel, A.","","2007","The retrieval of the earth's reflection response from cross?correlations of seismic noise recordings can provide valuable information, which may otherwise not be available due to limited spatial distribution of seismic sources. We cross?correlated ten hours of seismic background?noise data acquired in a desert area. The cross?correlation results show several coherent events, which align very well with reflections from an active survey at the same location. Therefore, we interpret these coherent events as reflections. Retrieving seismic reflections from background?noise measurements has a wide range of applications in regional seismology, frontier exploration and long?term monitoring of processes in the earth's subsurface.","cross-correlation; Green's function retrieval; reflections; interferometry","en","journal article","American Geophysical Union","","","","","","","","Civil Engineering and Geosciences","Geotechnology","","","","" "uuid:bc099609-47bd-4ad8-91ad-2a4a9a949c0f","http://resolver.tudelft.nl/uuid:bc099609-47bd-4ad8-91ad-2a4a9a949c0f","Seismic interferometry-turning noise into signal","Curtis, A.; Gerstoft, P.; Sato, H.; Snieder, R.; Wapenaar, C.P.A.","","2006","Turning noise into useful data—every geophysicist's dream? And now it seems possible. The field of seismic interferometry has at its foundation a shift in the way we think about the parts of the signal that are currently filtered out of most analyses—complicated seismic codas (the multiply scattered parts of seismic waveforms) and background noise (whatever is recorded when no identifiable active source is emitting, and which is superimposed on all recorded data). Those parts of seismograms consist of waves that reflect and refract around exactly the same subsurface heterogeneities as waves excited by active sources. The key to the rapid emergence of this field of research is our new understanding of how to unravel that subsurface information from these relatively complex-looking waveforms. And the answer turned out to be rather simple. This article explains the operation of seismic interferometry and provides a few examples of its application.","geophysical techniques; seismology; structural engineering; earthquakes; interferometry","en","journal article","Society of Exploration Geophysicists","","","","","","","","Civil Engineering and Geosciences","","","","","" "uuid:fba06a01-92fd-4ca6-bd0d-d801e53e4709","http://resolver.tudelft.nl/uuid:fba06a01-92fd-4ca6-bd0d-d801e53e4709","High-accuracy absolute distance metrology","Swinkels, B.L.","Braat, J.J.M. (promotor)","2006","Abstract not available","metrology; absolute distance measurement; interferometry; laser stabilization","en","doctoral thesis","","","","","","","","","Applied Sciences","","","","","" "uuid:c0512fe5-692e-47e3-98a2-a24cf29c0d09","http://resolver.tudelft.nl/uuid:c0512fe5-692e-47e3-98a2-a24cf29c0d09","Spurious multiples in seismic interferometry of primaries","Snieder, R.; Wapenaar, C.P.A.; Larner, K.","","2006","Seismic interferometry is a technique for estimating the Green's function that accounts for wave propagation between receivers by correlating the waves recorded at these receivers. We present a derivation of this principle based on the method of stationary phase. Although this derivation is intended to be educational, applicable to simple media only, it provides insight into the physical principle of seismic interferometry. In a homogeneous medium with one horizontal reflector and without a free surface, the correlation of the waves recorded at two receivers correctly gives both the direct wave and the singly reflected waves. When more reflectors are present, a product of the singly reflected waves occurs in the crosscorrelation that leads to spurious multiples when the waves are excited at the surface only. We give a heuristic argument that these spurious multiples disappear when sources below the reflectors are included. We also extend the derivation to a smoothly varying heterogeneous background medium.","interferometry; seismic waves; seismology","en","journal article","Society of Exploration Geophysicists","","","","","","","","Civil Engineering and Geosciences","Geotechnology","","","","" "uuid:fc9a5a03-cbfa-40ca-8f4d-9652ecd325f5","http://resolver.tudelft.nl/uuid:fc9a5a03-cbfa-40ca-8f4d-9652ecd325f5","Seismic interferometry: Reconstructing the earth's reflection response","Draganov, D.S.; Wapenaar, C.P.A.; Thorbecke, J.W.","","2006","In 1968, Jon Claerbout showed that the reflection response of a 1D acoustic medium can be reconstructed by autocorrelating the transmission response. Since then, several authors have derived relationships for reconstructing Green's functions at the surface, using crosscorrelations of (noise) recordings that were taken at the surface and that derived from subsurface sources.For acoustic media, we review relations between the reflection response and the transmission response in 3D inhomogeneous lossless media. These relations are derived from a one-way wavefield reciprocity theorem. We use modeling results to show how to reconstruct the reflection response in the presence of transient subsurface sources with distinct excitation times, as well as in the presence of simultaneously acting noise sources in the subsurface. We show that the quality of reconstructed reflections depends on the distribution of the subsurface sources. For a situation with enough subsurface sources — that is, for a distribution that illuminates the subsurface area of interest from nearly alldirections — the reconstructed reflection responses and the migrated depth image exhibit all the reflection events and the subsurface structures of interest, respectively. With only a few subsurface sources, that is, with insufficient illumination, the reconstructed reflection responses are noisy and can even become kinematically incorrect. At the same time, however, the depth image, which was obtained from their migration, still shows clearly all the illuminated subsurface structures at their correct positions.For the elastic case, we review a relationship between the reflection Green's functions and the transmission Green's functions derived from a two-way wavefield reciprocity theorem. Using modeling examples, we show how to reconstruct the different components of the particle velocity observed at the surface and resulting from a surface traction source. This reconstruciton is achieved using crosscorrelations of particle velocity components measured at the surface and resulting from separate P- and S-wave sources in the subsurface.","seismology; interferometry; seismic waves; Green's function methods","en","journal article","Society of Exploration Geophysicists","","","","","","","","Civil Engineering and Geosciences","Geotechnology","","","","" "uuid:68e13eb2-52e7-499c-8a04-ddee6fa0d6dd","http://resolver.tudelft.nl/uuid:68e13eb2-52e7-499c-8a04-ddee6fa0d6dd","Green's function representations for seismic interferometry","Wapenaar, C.P.A.; Fokkema, J.T.","","2006","The term seismic interferometry refers to the principle of generating new seismic responses by crosscorrelating seismic observations at different receiver locations. The first version of this principle was derived by Claerbout (1968), who showed that the reflection response of a horizontally layered medium can be synthesized from the autocorrelation of its transmission response. For an arbitrary 3D inhomogeneous lossless medium it follows from Rayleigh's reciprocity theorem and the principle of time-reversal invariance that the acoustic Green's function between any two points in the medium can be represented by an integral of crosscorrelations of wavefield observations at those two points. The integral is along sources on an arbitrarily shaped surface enclosing these points. No assumptions are made with respect to the diffusivity of the wavefield. The Rayleigh-Betti reciprocity theorem leads to a similar representation of the elastodynamic Green's function. When a part of the enclosing surface is the earth's free surface, the integral needs only to be evaluated over the remaining part of the closed surface. In practice, not all sources are equally important: The main contributions to the reconstructed Green's function come from sources at stationary points. When the sources emit transient signals, a shaping filter can be applied to correct for the differences in source wavelets. When the sources are uncorrelated noise sources, the representation simplifies to a direct crosscorrelation of wavefield observations at two points, similar as in methods that retrieve Green's functions from diffuse wavefields in disordered media or in finite media with an irregular bounding surface.","seismology; interferometry; seismic waves; Green's function methods","en","journal article","Society of Exploration Geophysicists","","","","","","","","Civil Engineering and Geosciences","Geotechnology","","","","" "uuid:aa105336-b322-48ad-b059-06baa3d2a96e","http://resolver.tudelft.nl/uuid:aa105336-b322-48ad-b059-06baa3d2a96e","Methods and sensors for accurate wavefront measurements","Soloviev, O.A.","French, P.J. (promotor)","2006","The wavefront measurement is an important part both in adaptive optics and in optical shop testing. A number of wavefront sensors based on interferometric or on Hartmann principle is known; this thesis investigates particular technologies that can help to increase the accuracy and/or speed of existing wavefront sensors either by optimising the wavefront reconstruction algorithm or by optimising the hardware. The topics discussed are interferogram analysis, optimising of the Hartmann mask geometry, and design of a 2D heterodyne phase detector.","wavefront; hartmann-shack; interferometry; lock-in pixel; high accuracy","en","doctoral thesis","","","","","","","","","Electrical Engineering, Mathematics and Computer Science","","","","","" "uuid:8a0a0986-5322-4c6d-a865-79893bfcda7d","http://resolver.tudelft.nl/uuid:8a0a0986-5322-4c6d-a865-79893bfcda7d","Nulling interferometry for exoplanet detection using polarization properties","Spronck, J.; Pereira, S.F.; Braat, J.J.M.","","2006","We present a new type of nulling interferometer that makes use of polarization properties to have on-axis destructive interference. The proposed design, which only involves commercial components and no achromatic device, is also suitable for internal modulation. This type of interferometer should enable a high rejection ratio in a theoretically unlimited spectral band. We implemented that concept on a two-beam white-light interferometer and we present here the first experimental results","interferometry; polarization; astronomical optics; nulling","en","conference paper","SPIE","","","","","","","","Applied Sciences","Optics Research Groep","","","","" "uuid:e2ecdb6a-d84b-4f18-a038-cf4833f5bf86","http://resolver.tudelft.nl/uuid:e2ecdb6a-d84b-4f18-a038-cf4833f5bf86","Nulling interferometry without achromatic phase shifters: Latest results","Spronck, J.; Pereira, S.F.; Braat, J.J.M.","","2006","We discuss the previously-reported measurements of a three-beam nulling interferometer without achromatic phase-shifters, using delay lines only. The theoretical rejection ratio of a few thousand has not been achieved experimentally. In order to explain the obtained results, some direct spectral and polarization measurements have been performed. We present here the latest results and discuss some asymmetries in the interference patterns.","interferometry; astronomical optics; nulling","en","conference paper","SPIE","","","","","","","","Applied Sciences","Optics Research Groep","","","","" "uuid:14b273f4-db17-4b3a-b655-9205318e0425","http://resolver.tudelft.nl/uuid:14b273f4-db17-4b3a-b655-9205318e0425","Polarization nulling interferometry for exoplanet detection","Spronck, J.; Pereira, S.F.; Braat, J.J.M.","","2006","We introduce a new concept of nulling interferometer without any achromatic device, using polarization properties of light. This type of interferometer should enable a high rejection ratio in a theoretically unlimited spectral band. We analyze several consequences of the proposed design, notably, the possibility of fast internal modulation.","interferometry; polarization; astronomical optics","en","journal article","Optical Society of America","","","","","","","","Applied Sciences","Imaging Science and Technology","","","","" "uuid:e4459301-2561-48e6-9d80-039274a124b5","http://resolver.tudelft.nl/uuid:e4459301-2561-48e6-9d80-039274a124b5","Chromatism compensation in wide-band nulling interferometry for exoplanet detection","Spronck, J.; Pereira, S.F.; Braat, J.J.M.","","2006","We introduce the concept of chromatism compensation in nulling interferometry that enables a high rejection ratio in a wide spectral band. Therefore the achromaticity condition considered in most nulling interferometers can be relaxed. We show that this chromatism compensation cannot be applied to a two-beam nulling interferometer, and we make an analysis of the particular case of a three-telescope configuration.","interferometry; astronomical optics","en","journal article","Optical Society of America","","","","","","","","Applied Sciences","Imaging Science and Technology","","","","" "uuid:9ab908f6-199f-4df9-83c1-9b66d4f9ed13","http://resolver.tudelft.nl/uuid:9ab908f6-199f-4df9-83c1-9b66d4f9ed13","Correcting movement errors in frequency-sweeping interferometry","Swinkels, B.L.; Bhattacharya, N.; Braat, J.J.M.","","2005","Absolute distance measurements can be performed with an interferometric method that uses only a single tunable laser. This method has one major drawback, because a small target movement of the order of one wavelength during a measurement will be interpreted as a movement of one synthetic wavelength. This effect is usually mitigated by adding a second (nonscanning) laser. We show that absolute distance measurements can be performed with only one laser if the movements encountered are smooth, on the time scale of one measurement. In this case the movement errors can be compensated with a simple algorithm that combines several subsequent measurements. First experimental results show good agreement with theory.","interferometry; phase measurement; lasers; tunable; laser range finder","en","journal article","Optical Society of America","","","","","","","","Applied Sciences","Imaging Science and Technology","","","","" "uuid:48cc617a-5771-4d64-b4aa-1915ac84084f","http://resolver.tudelft.nl/uuid:48cc617a-5771-4d64-b4aa-1915ac84084f","Comparison of blind imaging performance of Fizeau and Michelson type arrays for a partially resolved object","Van der Avoort, C.; Den Herder, J.W.; Braat, J.","","2005","This paper compares two well-known types of interferometer arrays for optical aperture synthesis. An analytical model for both types describes the expected output, in terms of photon counts. The goal is to characterize the performance of both types of array for blind imaging of a wide-field or extended object that would be partially resolved by a single elementary aperture. The spectrum of the source is assumed to be constant over the source and in time, but broad-banded. The light levels are such that only a few photons per pixel or bin are received. The simulated interferometer responses are discussed. The process of reconstructing the source from the ‘recorded’ responses is presented, but not discussed in this paper. It turns out that both types of interferometer are capable of imaging a partially resolved source with high spatial frequencies present all over the source.","interferometry; homothenic mapping; wide-field imaging; aperture synthesis","en","conference paper","SPIE","","","","","","","","Applied Sciences","Imaging Science and Technology","","","","" "uuid:197db690-96d8-4d86-9acc-7f1d3b5a8f28","http://resolver.tudelft.nl/uuid:197db690-96d8-4d86-9acc-7f1d3b5a8f28","CMOS integrator based lock-in pixel for heterodyne interferometry","Soloviev, O.; Vdovin, G.","","2005","This article presents a prototype of a CMOS phase sensor for high accuracy (1 Angstrom) heterodyne interferometry. Switched integrators realization of a lock-in pixel for 4-bucket phase detection algorithm is described and illustrated by experimental results. Factors that limit the accuracy of this implementation and possible ways for its improvement are discussed.","interferometry; EUV lithography; phase detection; lock-in pixel; CMOS","en","conference paper","SPIE","","","","","","","","Electrical Engineering, Mathematics and Computer Science","","","","","" "uuid:34936d75-bb7c-4531-b68d-bae2fcc61f99","http://resolver.tudelft.nl/uuid:34936d75-bb7c-4531-b68d-bae2fcc61f99","Measurements from a novel interferometer for EUVL mirror substrates","Krieg, M.L.; Braat, J.J.M.","","2005","A previously reported interferometer without intermediate optics is used to perform measurements on an aspherical extreme ultraviolet lithography mirror substrate. Acousto-optic modulation based phase shifting is used together with a novel phase retrieval algorithm to retrieve the phase distribution from our interferograms. The phase distribution is then processed by a previously reported inverse propagation algorithm to give the shape of the mirror under test. Our results are compared with measurements performed with conventional Fizeau interferometry and the discrepancies are discussed with reference to systematic error sources inherent in the classical and novel interferometers.","interferometry; EUVL; phase shifting; metrology","en","conference paper","SPIE","","","","","","","","Applied Sciences","Imaging Science and Technology","","","","" "uuid:51c0c555-699f-4de8-a0a4-995ec55fd28f","http://resolver.tudelft.nl/uuid:51c0c555-699f-4de8-a0a4-995ec55fd28f","Phase extraction from three interferograms with different unknown tilts","Soloviev, O.; Vdovin, G.","","2005","We propose an algorithm for phase retrieval from three interferograms which differ only by an arbitrary unknown tilt terms in the phase. The method is illustrated by examples.","interferometry; phase extraction; phase detection; interferogram analysis","en","conference paper","SPIE","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electronic Instrumentation Laboratory","","","","" "uuid:0e4cc0d3-ab56-4f79-8e4f-b968729e7f0f","http://resolver.tudelft.nl/uuid:0e4cc0d3-ab56-4f79-8e4f-b968729e7f0f","Michelson wide-field stellar interferometry: Principles and experimental verification","Montilla, I.; Pereira, S.F.; Braat, J.J.M.","","2005","A new interferometric technique for Michelson wide-field interferometry is presented that consists of a Michelson pupil-plane combination scheme in which a wide field of view can be achieved in one shot. This technique uses a stair-shaped mirror in the intermediate image plane of each telescope in the array, allowing for simultaneous correction of the differential delay for the on-axis and off-axis image positions. Experimental results in a laboratory setup show that it is possible to recover the fringes of on-axis and off-axis stars with an angular separation of 1 arc min simultaneously and with a similar contrast. This new technique represents a considerable extension of the field of view of an interferometer without the need for extra observation time.","instrumentation; measurement; metrology; interferometry; interference; astronomical optics; astronomy; astrophysics","en","journal article","Optical Society of America","","","","","","","","Applied Sciences","Imaging Science and Technology","","","","" "uuid:b4149e72-4a3e-4c2e-b6ba-76934129ce27","http://resolver.tudelft.nl/uuid:b4149e72-4a3e-4c2e-b6ba-76934129ce27","Absolute Heterodyne Interferometer for Strongly Aspherical Mirrors","Krieg, M.L.","Braat, J.J.M. (promotor)","2004","For the past thirty years, microchips have doubled in complexity every two years. This increasing complexity required that the size of the structures written on silicon halve at the same rate. A fundamentally limiting factor to the size of microchip structures is the wavelength of the lithographic projection processes used in their manufacture. Consequently, the wavelengths used to produce microchips have shrunk from 436nm, at the boundary of the visible spectrum, to 193nm, in the ultraviolet, between 1975 and 2002. A next generation process aims to use light with a wavelength of 13nm, in what is called extreme ultraviolet lithography (EUVL). Unlike previous processes, which could use lens systems to project the required patterns onto the microchips, EUVL requires the use of mirror projection systems. The mirrors used are highly aspheric and must be manufactured with unprecedented accuracies, of the order of 0.1nm. There are currently no affordable and easy to use systems to measure such mirrors with the required accuracy in optical workshops during manufacture. While the primary push for the development of such a measurement tool has come from the semiconductor industry, there are a number of other technology branches which could benefit from increased reflector accuracies. These include astronomy at ultra-short wavelengths, plasma physics, and biological microscopy. This thesis describes the construction and use of a novel interferometer to accurately measure the shape of such EUVL mirror substrates. Since tools to measure the surface roughness of these mirrors are readily available, we are concentrating on the measurement of spatial frequencies below 1mm-1 for the entire mirror surface. The main advantages of our interferometer over competing instruments are its independence from reference optics, which could introduce significant errors in other types of interferometers, its ability to measure the whole surface of most EUVL optics in one go and the possibility of using a more accurate type of interferometry - heterodyne interferometry - instead of the usual phase stepping. In contrast with a number of methods already available, this instrument is suitable for use in optical workshops, both in terms of cost and ease of use. Although the accuracy of 4nm reported here for our preliminary measurements falls short of the desired accuracy of 0.1nm, several improvements not yet implemented are likely to improve the accuracy of the instrument to desired levels. The most significant source of error at this time is believed to be the sensor. A sensor designed specifically to meet the requirements of our interferometer was still under development at the time of writing. In constructing the interferometer presented here, advances have been made in a number of fields: The novel nature of the interferometer required the development of a unique mathematical tool - an inverse propagation algorithm - to retrieve the shape of the surface under test from the measurement data. This has been achieved using a combination of analytic raytracing and numerical diffraction methods based on the idea of boundary diffracted waves, to obtain a good balance between computational speed and accuracy. A rigorous method for diffraction calculations was also developed and used to confirm the accuracy of the fast hybrid method finally used in the inverse propagation algorithm. The light source constructed is capable of providing a stable set of wavelengths which can be used to perform full-field multiple wavelength heterodyne interferometry at three wavelengths simultaneously. In the absence of a suitable sensor, the light source can also be used to perform sequential multiple wavelength interferometry using phase shifting methods. To ensure a minimum susceptibility to drift and vibrations, several optical mounting structures were re-designed from scratch. The custom designed mounts have been shown to outperform commercially available mounts. Two different types of sensors were tested and compared. A commercially available CCD sensor already allowed us to make measurements coming close to the desired accuracy by using calibration techniques to reduce the influence of a number of systematic error sources. A recently developed sensor, with phase-measuring active pixels, was used to demonstrate new approaches to interferometry: full-field heterodyne interferometry, as well as the beat frequency de-multiplexing of multiple wavelengths, allowing interferometry at several wavelengths simultaneously. An interferometer frame, which allows the stable placement of the mirror and various other components, has been designed and constructed entirely from invar to ensure optimum immunity against temperature fluctuations. Theoretical models were used to show that substrates with numerical apertures as large as 0.26 may be measured with the desired accuracy, limited only by the optical fibers used. Measurements carried out on the optical fibers showed that the sphericity of the wave fronts produced was in agreement with our theoretical models. By tapering and polishing the fiber ends, it may be possible to measure optics with even larger numerical apertures. Preliminary measurements of a test substrate, performed using phase shifting techniques and a standard CCD, yielded promising results. The measurement resulted in a retrieved mirror shape within 4.2nm rms of the nominal mirror shape, and an even smaller deviation from the mirror shape as measured by conventional interferometry techniques. The three main factors thought to limit the instrument's accuracy are the non-uniformity of the features on the CCD, the presence of a cover-glass on the sensor and insufficient a-priori knowledge of the relative positions of the interferometer components. All of these factors can be overcome or reduced, leading to measurements with the required accuracy in the foreseeable future. The result will be an ultra-precise metrology instrument suitable for use in optical workshops.","metrology; absolute; heterodyne; interferometry; euvl; aspherical mirrors","en","doctoral thesis","","","","","","","","","Applied Sciences","","","","","" "uuid:c2e72235-c88e-4047-8d78-abc3ddbc1744","http://resolver.tudelft.nl/uuid:c2e72235-c88e-4047-8d78-abc3ddbc1744","Michelson wide-field stellar interferometry","Montilla, I.","Braat, J.J.M. (promotor)","2004","The main goal of this thesis is to develop a system to permit wide field operation of Michelson Interferometers. A wide field of view is very important in applications such as the observation of extended or multiple objects, the fringe acquisition and/ or tracking on a nearby unresolved object, and also to reduce the observation time. For ground-based arrays, the field of view should be at least equal to the isoplanatic patch. Optical Stellar Interferometry consists of using two or more telescopes to collect the light from a distant object in order to obtain information with very high angular resolution. When two apertures are separated by a distance B, called baseline, the flat wavefront that comes from a distant source at a certain angle from the baseline does not reach the apertures at the same time. This delay will introduce an Optical Pathlength Difference (OPD) at both arms of the interferometer; if this path length difference is larger than the coherence length, then the light from both apertures will not interfere. In order to detect fringes over an extended field of view the OPD needs to be compensated before the beam combination takes place. In most interferometers nowadays this is done by means of delay lines. The light coming from an off-axis direction has a different delay than the light coming onaxis, referred to as differential delay. In so-called Fizeau interferometers, the synthetic aperture of the telescope array is exactly reproduced in a down-scaled version at the recombination optics; this recombination scheme has intrinsic path length compensation and a correspondingly wide field. This technique is very promising, but it is not useful if the baselines are very large compared to the single collector's aperture. In this case, the central peak is narrow and the energy is spread over the sidelobes of the interference pattern, limiting the sensitivity of the instrument. For non-Fizeau interferometers, the beams from the telescope array are simply overlapped (pupil-plane recombination) or combined in the image plane without maintaining the input pupil configuration. At angles where the differential delay becomes higher than the coherence length, the fringes disappear and the high-resolution information on the objects that are off-axis is lost. One way to solve this problem and acquire a wide field of view is to introduce a correction to the OPD for every angle in the telescope's field. In order to avoid the serious drawback of Fizeau interferometry at a large ratio of baseline over aperture size, we thought of a new approach to the problem, i.e., a system that could use a Michelson pupil-plane combination scheme but acquiring a wide field of view in one shot, saving also observation time. The functional principle of our approach is the introduction of an equalised OPD. This extra OPD can be translated in first-order approximation in steps of constant width and variable height which can be achieved by setting a stair-shaped mirror in an intermediate image plane of the interferometer. The focal plane has the characteristic that the light from different parts of the sky is focused separately, and for this reason we use it to introduce the equalization of the OPD. An extra OPD is introduced as a function of the field angle, so that coherent interference over a wide field of view can be obtained. The dimensions of the steps and the orientation of the mirror depends on the baseline and the pointing direction. Because the projection of the baseline vector on the entrance pupil changes with the hour angle during an astronomical observation, the mirror has to be actuated to follow these changes: it has to be rotated to follow the rotation of the projected baseline in order to maintain the steps perpendicular to it, and the depth must vary as it has to be adapted to the modulus of the projected baseline. In a system formed by more than two telescopes, it is necessary to have a step mirror at the focal plane of each telescope and a common reference point for the different baselines. Each mirror will be perpendicular to the projection of its baseline on the entrance pupil of its telescope. In this thesis we have studied the problem of the field of view for non-Fizeau arrays analytically and experimentally. The complete analytical description of a pupilplane interferometer with a staircase mirror in the focal plane of one of its arms is developed, and the results are compared with the experiments. We have designed a stair-shaped mirror that was placed in the focal plane of one of the arms of a twoarm Michelson-type interferometer. With a Xenon arc-lamp and a starmask we simulate different configurations of objects in the sky, with several off-axis objects with a differential delay that should be compensated by the staircase mirror. For all configurations, the experimental results followed the analytical predictions, and the visibility of the on-axis and off-axis objects was retrieved simultaneously. Special attention was given to the case of a star focused on the edge of a step. Analytical calculations and experiments show that in that case two sets of fringes, each corresponding to one step, are detected. By adding the information contained in this two fringes it is possible to retrieve the visibility of the source, meaning that no information is lost due to the discontinuous nature of the mirror, and a continuous wide field can be reconstructed.","interferometry; wide field; imaging","en","doctoral thesis","PrintPartners Ipskamp","","","","","","","","Applied Sciences","","","","","" "uuid:01e28763-f3f8-4edc-be69-086944919752","http://resolver.tudelft.nl/uuid:01e28763-f3f8-4edc-be69-086944919752","Experimental performance of homothetic mapping for wide field interferometric imaging","Van der Avoort, C.; Van Brug, H.; Den Herder, J.W.; d'Arcio, L.; Le Poole, R.; Braat, J.","","2004","Homothetic mapping is an aperture synthesis technique that allows interferometric imaging over a wide fieldof-view. A laboratory experiment was set up to demonstrate the feasibility of this technique. Here, we present the first static experiments on homothetic mapping that have been done on the Delft Testbed for Interferometry (DTI). Before a changeable telescope configuration is provided, we first took a fixed telescope configuration and tested the algorithms for their ability to provide an exit pupil configuration before beam combination, that was an exact copy of this telescope configuration. By doing so, we created a homothetic imaging system. This is an imaging system that acts as a masked aperture monolithic telescope, but consists of (in our case) three telescopes of which the light follow their own optical trains.","interferometry; homothetic mapping; wide field imaging; aperture synthesis","en","conference paper","SPIE","","","","","","","","Applied Sciences","Imaging Science and Technology","","","","" "uuid:ea2ceadb-a880-45f9-99c6-eb2a531082c5","http://resolver.tudelft.nl/uuid:ea2ceadb-a880-45f9-99c6-eb2a531082c5","Experimental verification of field extension for non-homothetic arrays with a pupil-plane interferometer","Montilla, I.; Pereira, S.F.; Braat, J.J.M.","","2004","Wide field interferometry has become a subject of increasing interest in the recent years. New methods have been suggested in order to avoid the drawbacks of the standard wide field method (homothetic mapping) which is not applicable when the aperture is highly diluted; for this reason imaging with non-homothetic arrays is being extensively studied1,2. The field of view of a pupil plane interferometer or a densified array consists only of a few resolution elements; in order to improve these systems, we developed a new method consisting of a Michelson pupil-plane combination scheme where a wide field of view can be achieved in one shot. This technique, called ""staircase mirror"" approach, has been described in a previous paper3 and uses a stair-shaped mirror in the intermediate image plane of each telescope in the array, allowing for simultaneous correction of the differential delay for the on and off-axis image positions. Experimental results have been obtained recovering the fringes of off-axis stars with an angular separation of approximately 1 arcmin simultaneously, and with a contrast similar to that of the on-axis reference star. With this example, we demonstrate an increase of the field of view by a factor of five, with no need of extra observation time. An algorithm to recover the visibilities from the stars focused on the edge of the steps is described and experimental results are shown that prove that a continuous wide field of view can be acquired in one shot.","interferometry; wide field imaging; aperture synthesis","en","conference paper","SPIE","","","","","","","","Applied Sciences","Imaging Science and Technology","","","","" "uuid:52ec7d6e-2da9-4f61-96f0-cc2222b683c5","http://resolver.tudelft.nl/uuid:52ec7d6e-2da9-4f61-96f0-cc2222b683c5","Demonstration of nulling using delay line phase shifters","Van der Avoort, C.; Mieremet, A.; Pereira, S.; Braat, J.","","2004","We present results of experiments obtained using a new nulling technique that enables deep nulling without the use of achromatic phase shifters. The experimental set-up consists of a three-beam interferometer that should provide a nulling depth of several thousands over a wavelength range of 500 to 650 nm. The intended depth of null was not achieved and further experiments on determining the spectrum of each beam revealed why. We describe a method of obtaining accurate beam spectra in a multi-beam interferometer. The insights on the need of spectral shape control were tested with our nulling theory and proved the sensitivity of this nulling approach with respect to spectral mismatches.","interferometry; nulling","en","conference paper","SPIE","","","","","","","","Applied Sciences","Imaging Science and Technology","","","","" "uuid:6aacb0cc-3851-48cb-b924-20d7496d245d","http://resolver.tudelft.nl/uuid:6aacb0cc-3851-48cb-b924-20d7496d245d","Inverse propagation algorithm for angstrom accuracy interferometer","Krieg, M.L.; Braat, J.J.M.","","2004","This paper will illustrate several approaches to retrieving the shape of aspherical reflective surfaces as used in EUV Lithography, from measurements from a previously reported angstrom-accuracy interferometer. First, the working principles of the interferometer will be reviewed, and typical measurement data expected from the instrument will be presented. Several methods will then be introduced for retrieving the reflector shape from such measurements. These methods will include approaches based on ray tracing, approximate diffraction calculations, and linearization of rigorous diffraction calculations which use a novel numerical scheme to reduce calculation time of the diffraction integral. The methods will be compared on the basis of accuracy, calculation time and extendibility.","inverse propagation; diffraction integral; ray tracing; interferometry","en","conference paper","SPIE","","","","","","","","Applied Sciences","Imaging Science and Technology","","","","" "uuid:772d751a-896b-4db0-b9b6-ccdfbfac1cd7","http://resolver.tudelft.nl/uuid:772d751a-896b-4db0-b9b6-ccdfbfac1cd7","Design of a Michelson Interferometer for Quantitative Refraction Index Profile Measurements","Nijholt, J.L.M.","","1998","This book describes the theoretical design of a three camera Michelson interferometer set-up for quantitative refractive index measuerments. Although a two camera system is easier to align and less expensive, a three camera interferometer is preferred because the expected measuring accuracy is much better. Here analytical expressions are found for the calculation of the required alignment accuracy of the interferometer's components: three CCD-cameras (six degrees of freedom each), a quarter wave plate (one degree of freedom) and a polariser (one degree of freedom). Also the required accuracy in the normalization of the intensity levels on the CCD-cameras is calculated.","interferometry; multy camera interferometer; positioning accuracy","en","book","Delft University Press","","","","","","","","Aerospace Engineering","","","","","" "uuid:b3bbb293-d473-4e23-994b-2137c6050c07","http://resolver.tudelft.nl/uuid:b3bbb293-d473-4e23-994b-2137c6050c07","Experimental and computational study of a blunt cylinder-flare model in high supersonic flow","Houtman, E.M.; Bannink, W.J.; Timmerman, B.H.","","1995","","Euler method; interferometry; high-supersonic flows; shock-shock interactions","en","report","Delft University of Technology","","","","","","","","Aerospace Engineering","","","","",""