Phase retrieval via propagation-based interferometry

We present an extension of the Gerchberg-Saxton algorithm to allow for phase retrieval from interferometric data recorded at multiple sample-detector distances. A system of coupled waves is introduced where the information exchange can be controlled by use of relaxation parameters. Optimal parameters are investigated by numerical simulation and demonstrated to work with experimental data. We demonstrate that systematic errors such as pointing instabilities of the interfering waves involved and position uncertainties of the detector can be overcome by dimensional extension of the search space. Further it is shown that the proposed approach offers superior reconstruction quality as compared to conventional Gerchberg-Saxton type algorithms. We expect that the method described here will open up numerous possibilities for the correction of systematic errors in optical phase retrieval and lensless microscopy

A phase retrieval algorithm based on three-dimensionally translated diffraction patterns55 S.)

An iterative phase retrieval method is proposed that combines alternating projections and registration of three-dimensionally translated near-field diffraction patterns. This method allows to enhance resolution limited by a finite detector size and automatically stitches the assembled data while avoiding the need for a priori knowledge or scanning of the object as encountered in coherent diffraction imaging or ptychography

Thin film substrates from the Raman spectroscopy point of view

We have investigated ten standard single crystal substrates of complex oxides on the account of their applicability in the Raman spectroscopy-based thin film research. In this study, we suggest a spectra normalization procedure that utilizes a comparison of the substrate\u27s Raman spectra to those of well-established Raman reference materials. We demonstrate that MgO, LaGaO 3, (LaAlO3)0.3(Sr2AlTaO 6)0.7 (LSAT), DyScO3, YAlO3, and LaAlO3 can be of potential use for Raman-based thin film research. At the same time TiO2 (rutile), NdGaO3, SrLaAlO4, and SrTiO3 single crystals exhibit multiple phonon modes accompanied by strong Raman background that substantially hinder Raman-based thin film experiments. Copyright © 2014 John Wiley & Sons, Ltd

Generation and characterization of focused helical x ray beams

The phenomenon of orbital angular momentum (OAM) affects a variety of important applications in visible optics, including optical tweezers, free-space communication, and 3D localization for fluorescence imaging. The lack of suitable wavefront shaping optics such as spatial light modulators has inhibited the ability to impart OAM on x-ray and electron radiation in a controlled way. Here, we report the experimental observation of helical soft x-ray beams generated by holographically designed diffractive optical elements. We demonstrate that these beams rotate as a function of propagation distance and measure their vorticity and coherent mode structure using ptychography. Our results establish an approach for controlling and shaping of complex focused beams for short wavelength scanning microscopy and OAM-driven applications

High-resolution wavefront sensing and aberration analysis of multi-spectral extreme ultraviolet beams

Coherent multi-spectral extreme ultraviolet beams have great potential for providing high spatial and temporal resolution for microscopy and spectroscopy applications. But due to the limitations of short-wavelength optics and the broad bandwidth, it remains a challenge to perform quantitative, high-resolution beam characterization. Here we present a wavefront sensing solution based on multiplexed ptychography, with which we show spectrally resolved, high-resolution beam reconstructions. Furthermore, using these high-fidelity quantitative wavefront measurements, we investigate aberration transfer mechanisms in the high-harmonic-generation process, where we present and explain harmonic-order-dependent astigmatism inheritance from the fundamental wavefront. This ptychographic wavefront sensing concept thus enables detailed studies of the high-harmonic-generation process, such as spatiotemporal effects in attosecond pulse formation