Light control in dynamic scattering media, like living tissues, is of paramount importance in biomedical imaging.
Although iterative wavefront shaping algorithms can focus light through dynamic media, more complicated tasks like transmission of arbitrary fields and energy delivery require longer calibration procedures, typically involving the measurement of the transmission matrix.
We report and showcase the performance of an optimization routine, based on a conventional wavefront shaping setup, allowing the online and recursive estimation of the transmission matrix of scattering media. Because it combines the benefits of iterative and transmission-matrix based algorithms, it enables full light control through dynamic and noisy environments.
Combining synthetic aperture approaches with reference-less setups, ptychography is a promising phase retrieval technique for label-free quantitative phase imaging. Within the phase retrieval community, spectral methods are known to accelerate gradient descent schemes, however their positive effect on experimental ptychographic datasets has not been proved.
Inspired by the latest theories on optimal spectral estimation, we achieved 3 times faster ptychographic reconstructions than with a standard gradient descent algorithm, in both simulations and experiments. The algorithms and experimental parameters crucially impacting the convergence speed are discussed.
We believe that spectral methods will help improve both theoretical understanding and experimental implementations of ptychography.
We present a study on the resolution limits and resolution factors of terahertz (THz) ptychography. Simulations of a binary amplitude object show that ptychography shares the same intrinsic resolution factors with digital holography, i.e. it is diffraction-limited. Reconstructions of amplitude and phase objects obtained from holographic and ptychographic experiments are comparable. A lateral resolution of around one wavelength λ is achieved on an amplitude object, while a depth resolution of around λ/5 is reported on a weakly diffracting phase object. THz ptychography is expected to complement THz holography for imaging biological samples and THz transparent specimens.
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