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Holotomography is an extension of computed tomography where samples with low X-ray absorption can be investigated with higher contrast. In order to achieve this, the imaging system must yield an optical resolution of a few micrometers or less, which reduces the measurement area (field of view = FOV) to a few mm at most. If the sample size, however, exceeds the field of view (called local tomography or region of interest = ROI CT), filter problems arise during the CT reconstruction and phase retrieval in holotomography. In this paper, we will first investigate the practical impact of these filter problems and discuss approximate solutions. Secondly, we will investigate the effectiveness of a technique we call "multiscalar holotomography", where, in addition to the ROI CT, a lower resolution non-ROI CT measurement is recorded. This is used to avoid the filter problems while simultaneously reconstructing a larger part of the sample, albeit with a lower resolution in the additional area. [ABSTRACT FROM AUTHOR]

Transparent crystalline scintillators such as cerium-doped YAG or LuAG are widely used in X-ray imaging for the indirect detection of X-rays. The application of reflective coatings on the front side to improve the optical gain is common practice for flat panel detectors with CsI or Gd 2 O 2 S powder scintillators but still largely unknown for crystalline scintillators such as LuAG. This work shows experimentally and quantitatively how a black and reflective coating on the X-ray side of a 2 mm LuAG:Ce scintillator improves the image quality compared to a 2 mm LuAG:Ce scintillator without a coating. The measurements have been done for two different distances, with 2 m and 29.7 m on the BM18 beamline of the European Synchrotron. The Modulation Transfer Function (MTF) and the Signal-to-Noise-Ratio (SNR 2 ) power spectrum as well as contrast-to-noise ratio are used for comparing image quality. Propagation-based phase contrast strongly enhances the SNR 2 amplitudes (gain ≈10 from 2 m to 29.7 m object-detector distance) of the raw images' spectrum independent of the scintillator coating. For both detector positions, the reflective coating is able to raise SNR 2 by up to 80% through the improved optical gain, while black coating does the opposite (decrease SNR 2 by 20%) with respect to no coating. With the tested optical setups, changes in MTF /sharpness between the coatings are minor. Comparing CNR 2 in CT scans of a multi-material sample, in this case an electric motor, we observe the reflective coating yielding better material contrast for plastic and air. Application and effect of Wiener-deconvolution, along with Paganin-type phase retrieval, are also discussed in the context of CT image quality.

Optically active spin defects are promising candidates for solid-state quantum information and sensing applications. To use these defects in quantum applications coherent manipulation of their spin state is required. Here, we realize coherent control of ensembles of boron vacancy centers in hexagonal boron nitride (hBN). Specifically, by applying pulsed spin resonance protocols, we measure a spin-lattice relaxation time of 18 microseconds and a spin coherence time of 2 microseconds at room temperature. The spin-lattice relaxation time increases by three orders of magnitude at cryogenic temperature. By applying a method to decouple the spin state from its inhomogeneous nuclear environment the optically detected magnetic resonance linewidth is substantially reduced to several tens of kilohertz. Our results are important for the employment of van der Waals materials for quantum technologies, specifically in the context of high resolution quantum sensing of two-dimensional heterostructures, nanoscale devices, and emerging atomically thin magnets., (Copyright © 2021 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC).)