arXiv subjects

Brad D. Price

Publications and source records attributed to Brad D. Price.

3 recordsLinked to original sources

arXiv2026

Fast and bright scintillators for ultrafast materials dynamics using 4th generation synchrotron

We present recent advances in fast and bright scintillators for ultrafast X-ray phase contrast imaging of dynamic materials experiments at the upgraded Advanced Photon Source (APS-U), a fourth generation synchrotron. APS-U enables hard X-ray imaging at frame rates of at least 13 MHz (corresponding to 77 ns or shorter interframe intervals), creating a new need for scintillators with faster response and higher light output than lutetium yttrium oxyorthosilicate (LYSO). For indirect imaging and diffraction with ultrafast cameras, commercial lanthanum bromide (LaBr3) and cerium bromide (CeBr3) are promising candidates. These materials exhibit decay times approximately a factor of two shorter than LYSO (around 40 ns) and lutetium oxyorthosilicate (LSO), while maintaining comparable light yield per incident X-ray photon. However, their implementation at APS-U requires addressing several challenges, including material limitations due to hygroscopicity, efficient optical coupling to imaging systems, and high quantum efficiency for conversion of scintillation light, predominantly at wavelengths below 400 nm, into detectable electronic signals. We report results from material characterization, detector integration and packaging, and beamline experiments of materials with impact. In addition, emerging scintillator classes, including perovskites and high-entropy materials, are discussed as potential alternatives for next-generation ultrafast X-ray diagnostics.

physics.ins-det↗

arXiv2025

Two-fluid mobility model from coupled hydrodynamic equations for simulating laser-driven semiconductor switches

We introduce a two-fluid mobility model incorporating fundamental aspects of electron-hole (e-h) scattering such as momentum conservation for simulating laser-driven semiconductor switches (LDSSs). Compared to previous works that use Matthiessen's rule, the two-fluid mobility model predicts distinct AC responses of e-h plasmas in semiconductors. Based on the two-fluid mobility model, we develop a theory with very few adjustable parameters for simulating the switching performance of LDSSs based on high-purity indirect-gap semiconductors such as silicon (Si). As a prototypical application, we successfully reproduce experimentally measured reflectance at around 320 GHz in a laser-driven Si switch. By injecting e-h plasmas with densities up to $10^{20}\,\rm cm^{-3}$, we reveal the importance of carrier-screening effects in e-h scattering and Auger recombination for carrier densities above the critical carrier density for exciton-plasma Mott transition. Our results also suggest a way to characterize the intrinsic momentum-relaxation mechanism, e-h scattering, and the intrinsic e-h recombination mechanism in indirect-gap semiconductors, Auger recombination. We reassess the ambipolar Auger coefficient of high-purity Si with high injection levels of e-h plasmas up to $10^{20}\,\rm cm^{-3}$ and find a minimal value of $1.8\times10^{-41}\,{\rm cm^6/ns}$. The value is more than one order of magnitude smaller than the ambipolar Auger coefficient widely used for simulating LDSSs, $3.8\times10^{-40}\,{\rm cm^6/ns}$, which was deduced from minority-carrier lifetime in highly doped silicon more than four decades ago.

cond-mat.mtrl-sci↗

arXiv2023

Order-of-Magnitude SNR Improvement for High-Field EPR Spectrometers via 3D-Printed Quasioptical Sample Holders

In this paper, we present a rapidly-prototyped, costefficient, 3D-printed quasioptical sample holder for improving the signal-to-noise ratio (SNR) in modern, resonator-free, highfield electron paramagnetic resonance (EPR) spectrometers. Such spectrometers typically operate in induction mode: the detected EPR (cross-polar) signal is polarized orthogonal to the incident (co-polar) radiation. The sample holder improves SNR in three modes: continuous wave, pulsed, and rapid-scan. An adjustable sample positioner allows for optimizing sample position to maximize the 240 GHz magnetic field B1, and a rooftop mirror allows for small rotations of the cross-polar signal to maximize the signal and minimize the co-polar background. When optimized, the co-polar isolation (the ratio of incident to detected co-polar signal) was around 50 dB, an improvement of over 20 dB. This large isolation is especially beneficial for maximizing the SNR of rapidscan EPR, but also improves the SNR in pulsed and cwEPR experiments. Through minimal modification, the sample holder may be incorporated into a variety of homebuilt, induction-mode hfEPR spectrometers in order to significantly improve the SNR (approx. 6x), and thereby reduce the acquisition time (by more than a factor of 30).

physics.ins-det↗