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.