Pages
 1
 2
 document

Alaifari, Rima (author), Bartolucci, F. (author), Steinerberger, Stefan (author), Wellershoff, Matthias (author)Gabor phase retrieval is the problem of reconstructing a signal from only the magnitudes of its Gabor transform. Previous findings suggest a possible link between unique solvability of the discrete problem (recovery from measurements on a lattice) and stability of the continuous problem (recovery from measurements on an open subset of R<sup>2...journal article 2024
 document

Cools, Liam (author)Counteracting image quality degradation caused by phase aberrations through physical correction requires the phase field to be known. As imaging hardware captures realvalued intensity, defined as the wave amplitude squared, obtaining this lost phase information is known as the phase retrieval problem and is a nonlinear and nonconvex...master thesis 2023
 document

Shen, Dong (author)Deformable Mirror (DM) is the key part in the AO system. Characterization of DM is important as it maps between input voltage signal and output mirror deformation. The precision of characterization largely affects the control performance. While characterizing the DM with wavefront sensors is easy and straightforward, there is very few research...master thesis 2023
 document

Alaifari, Rima (author), Bartolucci, F. (author), Wellershoff, Matthias (author)Sampled Gabor phase retrieval — the problem of recovering a squareintegrable signal from the magnitude of its Gabor transform sampled on a lattice — is a fundamental problem in signal processing, with important applications in areas such as imaging and audio processing. Recently, a classification of squareintegrable signals which are not phase...conference paper 2023
 document

Ansuinelli, P. (author)The importance of inverse problems is paramount in science and physics because their solution provides information about parameters that cannot be directly observed. This thesis discusses and details the application of a few inverse methods in optical imaging, metrology and inspection of lithographic targets, particularly patterned structures on...doctoral thesis 2022
 document

Soloviev, O.A. (author), Noom, J. (author), Nguyen, Hieu Thao (author), Vdovin, Gleb (author), Verhaegen, M.H.G. (author)We investigate the general adjustment of projectionbased phase retrieval algorithms for use with saturated data. In the phase retrieval problem, model fidelity of experimental data containing a nonzero background level, fixed pattern noise, or overexposure, often presents a serious obstacle for standard algorithms. Recently, it was shown...conference paper 2022
 document

Liu, Runfei (author)Phase Retrieval Problem is very common and has a lot of applications in fields such as microscope, astronomy, crystallography, optical imaging etc.. In this problem, PSF and the pupil function are given, and the goal is to reconstruct the phase of the object. For camera which has 8 bits color depth, the maximum number of colors that can be...master thesis 2021
 document

Nguyen, Hieu Thao (author), Soloviev, O.A. (author), Verhaegen, M.H.G. (author)We present the convergence analysis of convex combination of the alternating projection and Douglas–Rachford operators for solving the phase retrieval problem. New convergence criteria for iterations generated by the algorithm are established by applying various schemes of numerical analysis and exploring both physical and mathematical...journal article 2021
 document

Nguyen, Hieu Thao (author), Soloviev, O.A. (author), Luke, Russell (author), Verhaegen, M.H.G. (author)We develop for the first time a mathematical framework in which the class of projection algorithms can be applied to high numerical aperture (NA) phase retrieval. Within this framework, we first analyze the basic steps of solving the highNA phase retrieval problem by projection algorithms and establish the closed forms of all the relevant...journal article 2021
 document

Trevisan, E. (author)Microscopic imaging has a resolution that is often far from the diffraction limit due to aberrations induced by the optics or by the sample itself. It is therefore of interest sensing these aberrations either directly or indirectly to improve image quality in postprocessing or with adaptive optics. To avoid the use of extra hardware, several...master thesis 2020
 document

Konijnenberg, A.P. (author)In this thesis, several phase retrieval methods are discussed. Since the focus will mainly be on theory rather than experiment, the structure has been determined by the similarities and differences of the mathematics of these methods. For example, a distinction is made between noniterative and iterative methods, and between singleshot...doctoral thesis 2019
 document

Doelman, R. (author)Aberrations in optical systems, such as telescopes and microscopes, degrade the quality of the images that can be produced by these systems. For example, an object that is positioned out of focus produces a blurred image on a camera sensor and the turbulent air in the earth’s atmosphere reduces the imaging performance of telescopes. In this...doctoral thesis 2019
 document

Noppen, Marko (author)Adaptive optics are widely used to correct the wavefront distortion imposed by atmospheric turbulence. Focal plane phase retrieval from intensity measurements has advantages due to the ease of implementation, potential broader application, less computations, low cost, high system bandwidth, simpliﬁed hardware and less calibration. To cope with...master thesis 2019
 document

Dwivedi, P. (author)Lenses are indispensable tool to perform imaging and see the small details of an object which was otherwise not possible. The smallest feature of an object that one can see using a lens depends on the numerical aperture (NA) of the lens and the used wavelength of light. For a fixed NA, the shorter the wavelength is, the smaller the features of...doctoral thesis 2019
 document

Dwivedi, P. (author), Pereira, S.F. (author), Urbach, Paul (author)Wavefront aberration measurements are required to test an extreme ultraviolet (EUV) imaging system. For a highNA EUV imaging system, where conventional wavefrontsensing techniques show limitations, ptychography can be used for this purpose. However, at the wavelength region of EUV (i.e., 13.5 nm), the position accuracy of the scanning mask...journal article 2019
 document

Ansuinelli, P. (author), Coene, W.M.J.M. (author), Urbach, Paul (author)EUV lithography is the main candidate for patterning of future technology nodes. Its successful implementation depends on many aspects, among which the availability of actinic mask metrology tools able to inspect the patterned absorber in order to control and monitor the lithographic process. In this work, we perform a simulation study to...conference paper 2019
 document

Dwivedi, P. (author), Konijnenberg, A.P. (author), Pereira, S.F. (author), Meisner, J.A. (author), Urbach, Paul (author)Ptychography is a form of coherent diffractive imaging; it employs farfield intensity patterns of the object to reconstruct the object. In ptychography, an important limiting factor for the reconstructed image quality is the uncertainty in the probe positions. Here, we propose a new approach which uses the hybrid inputoutput algorithm and...journal article 2019
 document

Konijnenberg, A.P. (author), Coene, W.M.J.M. (author), Urbach, Paul (author)A noiserobust extension of iterative phase retrieval algorithms that does not need to assume a noise model is proposed. It works by adapting the intensity constraints using the reconstructed object. Using a proofofprinciple ptychographic experiment with visible light and a spatial light modulator to create an object, the proposed method is...journal article 2018
 document

Gupta, Abhimanyu (author)The use of radial basis function (RBF) expansion as a means to represent the generalized pupil function for aberration retrieval from intensity pointspread function has been investigated in this research article. The optimal choice of RBF hyperparameters is derived empirically to achieve an increased accuracy of approximation along with well...master thesis 2017
 document

Konijnenberg, A.P. (author)An overview of several ptychographic phase retrieval methods and the theory behind them is presented. By looking into the theory behind more basic singleintensity pattern phase retrieval methods, a theoretical framework is provided for analyzing ptychographic algorithms. Extensions of ptychographic algorithms that deal with issues such as...journal article 2017
Pages
 1
 2