arXiv subjects

Maik Kahnt

Publications and source records attributed to Maik Kahnt.

6 recordsLinked to original sources

arXiv2025

Optimizing probes for multi-beam ptychography

Multi-beam ptychography (MBP) offers a scalable solution to improve the throughput of state-of-the-art ptychography by increasing the number of coherent beams that illuminate the sample simultaneously. However, increasing the number of beams in ptychography makes ptychographical reconstructions more challenging and less robust. It has been demonstrated that MBP reconstructions can be made more robust by using well-structured and mutually separable probes. Here, we present a quantitative framework to assess probe sets based on separability, uniformity, and fabrication feasibility. We show that Hadamard-based binary phase masks consistently outperform Zernike polynomials, experimentally feasible phase plates, and spiral phase masks across varying scan densities. While spiral masks yield comparable resolution, they scale less efficiently due to increased structural complexity. Our results establish practical criteria for evaluating and designing structured probes to enable more robust and scalable implementation of MBP in high-throughput coherent X-ray and EUV imaging.

physics.optics↗

arXiv2025

Scanning diffraction imaging without stable illumination and scan position information

Ptychography has become prominent at synchrotron facilities worldwide for characterizing biological and material specimens' topological structures and properties at the nanometer or atomic scale, due to its lens - less, highly quantitative phase imaging. Its high - resolution imaging depends on accurate lateral scan position info, a large overlap ratio, and a stable probe function. But as research moves to atomic scales, meeting these requirements gets harder, often needing high - precision motion control and manual pre - calibration. This paper presents a new imaging framework. By adding a wavefront modulator and a new phase retrieval workflow, it removes the strict requirements of traditional ptychography. Significantly, our method doesn't need pre - calibration of the wavefront modulator. Optical validation showed the deviation between the recovered position and a top - tier motion stage was less than 10 nm. Sub - pixel position accuracy was achievable even with a 13% overlap ratio. In an X - ray experiment with a spatially unstable probe violating the ptychographic model and an 18% overlap ratio, our method simultaneously and quantitatively retrieved beam spatial deviation, scan position, probe function, and sample transmission function. Notably, it measured probe spatial deviations of 500nm along the X - axis and 50nm along the Y - axis, which is not feasible by previous methods. With these experimentally proven advantages, we anticipate our method to be a powerful imaging tool with auto - quantitative calibration of various parameters. It will simplify scanning diffraction microscopy implementation and expand its application scope, especially in nanometer and atomic scale imaging.

eess.IV↗

arXiv2024

X-ray multibeam ptychography at up to 20 keV: nano-lithography enhances X-ray nano-imaging

Non-destructive nano-imaging of the internal structure of solid matter is only feasible using hard X-rays due to their high penetration. The highest resolution images are achieved at synchrotron radiation sources (SRF), offering superior spectral brightness and enabling methods such as X-ray ptychography delivering single-digit nm resolution. However the resolution or field of view is ultimately constrained by the available coherent flux. To address this, the beam's incoherent fraction can be exploited using multiple parallel beams in an approach known as X-ray multibeam ptychography (MBP). This expands the domain of X-ray ptychography to larger samples or more rapid measurements. Both qualities favor the study of complex composite or functional samples, such as catalysts, energy materials, or electronic devices. The challenges of performing ptychography at high energy and with many parallel beams must be overcome to extract the full advantages for extended samples while minimizing beam attenuation. Here, we report the application of MBP with up to 12 beams and at photon energies of 13 and 20 keV. We demonstrate performance for various samples: a Siemens star test pattern, a porous Ni/\ce{Al2O3} catalyst, a microchip, and gold nano-crystal clusters, exceeding the measurement limits of conventional hard X-ray ptychography without compromising image quality.

physics.app-ph↗

arXiv2024

3D Imaging of Magnetic Domains in Nd2Fe14B using Scanning Hard X-Ray Nanotomography

Nanoscale structural and electronic heterogeneities are prevalent in condensed matter physics. Investigating these heterogeneities in three dimensions (3D) has become an important task for understanding their material properties. To provide a tool to unravel the connection between nanoscale heterogeneity and macroscopic emergent properties in magnetic materials, scanning transmission X-ray microscopy (STXM) is combined with X-ray magnetic circular dichroism (XMCD). A vector tomography algorithm has been developed to reconstruct the full 3D magnetic vector field without any prior assumptions or knowledge. 2D STXM projections of single crystalline \ndfeb\ pillars are recorded for two different sample tilt angles while rotating around the vertical tomographic axis using $120$ nm X-ray beams with left and right circular polarization. Image alignment and iterative registration has been implemented, based on the 2D STXM projections for the two tilts. Dichroic projections obtained from difference images are used for the tomographic reconstruction to obtain the 3D magnetization distribution at the nanoscale.

physics.comp-ph↗

arXiv2019

A direct solver for the phase retrieval problem in ptychographic imaging

Measurements achieved with ptychographic imaging are a special case of diffraction measurements. They are generated by illuminating small parts of a sample with, e.g., a focused X-ray beam. By shifting the sample, a set of far-field diffraction patterns of the whole sample are then obtained. From a mathematical point of view those measurements are the squared modulus of the windowed Fourier transform of the sample. Thus, we have a phase retrieval problem for local Fourier measurements. A direct solver for this problem was introduced by Iwen, Viswanathan and Wang in 2016 and improved by Iwen, Preskitt, Saab and Viswanathan in 2018. Motivated by the applied perspective of ptychographic imaging, we present a generalization of this method and compare the different versions in numerical experiments. The new method proposed herein turns out to be more stable, particularly in the case of missing data.

math.NA↗

arXiv2018

Ptychographic characterization of polymer compound refractive lenses manufactured by additive technology

The recent success in the development of high precision printing techniques allows one to manufacture free-standing polymer structures of high quality. Two-photon polymerization lithography is a mask-less technique with down to 100 μm resolution that provides full geometric freedom. It has recently been applied to the nanofabrication of X-ray compound refractive lenses (CRLs). In this article we report on the characterization of two sets of CRLs of different design produced by two-photon polymerization induced lithography.

physics.optics↗