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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
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Alaifari, Rima (author), Bartolucci, F. (author), Wellershoff, Matthias (author)Sampled Gabor phase retrieval — the problem of recovering a square-integrable 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 square-integrable signals which are not phase...conference paper 2023
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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
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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 projection-based phase retrieval algorithms for use with saturated data. In the phase retrieval problem, model fidelity of experimental data containing a non-zero background level, fixed pattern noise, or overexposure, often presents a serious obstacle for standard algorithms. Recently, it was shown...conference paper 2022
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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 high-NA phase retrieval problem by projection algorithms and establish the closed forms of all the relevant...journal article 2021
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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
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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 non-iterative and iterative methods, and between single-shot...doctoral thesis 2019
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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
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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
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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
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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 far-field 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 input-output algorithm and...journal article 2019
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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 high-NA EUV imaging system, where conventional wavefront-sensing 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
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Konijnenberg, A.P. (author), Coene, W.M.J.M. (author), Urbach, Paul (author)A noise-robust 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 proof-of-principle ptychographic experiment with visible light and a spatial light modulator to create an object, the proposed method is...journal article 2018
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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 single-intensity 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
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Konijnenberg, A.P. (author)We have designed a ptychographical algorithm (HIO-PIE) in which HIO (Hybrid Input-Output) iterations are applied for each probe position sequentially. Simulations indicated that HIO-PIE tends to outperform PIE (Ptychographical Iterative Engine) even in the presence of shot noise, especially when the number of probe positions is small. Thus, this...conference paper 2017
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Dwivedi, P. (author), Konijnenberg, A.P. (author), Pereira, S.F. (author), Urbach, Paul (author)For high resolution imaging, X-rays and electron beams are being used. However, for such a short wavelength, imaging with lenses becomes difficult as lenses absorb a part of radiation and lenses with very low aberrations must be used. Ptychography is a lens-less imaging technique which uses intensity information of the multiple diffraction...conference paper 2017
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Konijnenberg, A.P. (author), Coene, W.M.J.M. (author), Urbach, Paul (author)We report on a novel non-iterative phase retrieval method with which the complex-valued transmission function of an object can be retrieved with a non-iterative computation, with a limited number of intensity measurements. The measurements are taken in either real space or Fourier space, and for each measurement the phase in its dual space is...journal article 2016
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Konijnenberg, A.P. (author), Coene, W.M.J.M. (author), Pereira, S.F. (author), Urbach, Paul (author)In this article we combine the well-known Ptychographical Iterative Engine (PIE) with the Hybrid Input-Output (HIO) algorithm. The important insight is that the HIO feedback function should be kept strictly separate from the reconstructed object, which is done by introducing a separate feedback function per probe position. We have also...journal article 2016
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Gong, H. (author), Pozzi, P. (author), Soloviev, O.A. (author), Verhaegen, M.H.G. (author), Vdovin, Gleb (author)We present a reference-less and time-multiplexing phase retrieval method by making use of the digital micromirror device (DMD). In this method, the DMD functions not only as a flexible binary mask which modulates the optical field, but also as a sampling mask for measuring corresponding phases, which makes the whole setup simple and robust. The...conference paper 2016
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Vdovin, Gleb (author), Gong, H. (author), Soloviev, O.A. (author), Pozzi, P. (author), Verhaegen, M.H.G. (author)We have experimentally demonstrated a lensless coherent microscope based on direct registration of the complex optical field by sampling the pupil with a sequence of two-point interferometers formed by a digital micromirror device. Complete registration of the complex amplitude in the pupil of the imaging system, without any reference beam,...journal article 2015
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