Md Kazi Rokunuzzaman | Searcharxiv

arXiv2026

Nonlinear Photocurrent Spectroscopy and Polarization-Tunable Shift Current in the Layered Semiconductor $\mathrm{CuScP_2S_6}$

The class of layered metal thiophosphates and selenophosphates are emerging as promising candidates for non-linear photonic and optoelectronic applications. Here we report one-photon absorption (1PA) and two-photon absorption (2PA) induced photocurrents in $CuScP_2S_6$, establishing it as an optoelectronically-active non-centrosymmetric semiconductor. Spectrally-resolved 1PA and 2PA photoresponsivity paired with photoluminescence and differential reflectance measurements reveal a band gap of 2.35 eV, several higher energy interband transitions, and sub-band gap multiphoton excitonic transitions. Vertical graphite/$CuScP_2S_6$/graphite devices exhibit zero-bias photocurrent with a polarity controlled by both photon energy and optical polarization orientation within the ab-plane. This sign-dependence combined with a characteristic power-law transition from linear to square-root scaling are consistent with a shift-current origin to this bulk photovoltaic effect (BPVE). These findings establish $CuScP_2S_6$ as a multi-functional platform for polarization-sensitive non-linear optoelectronics.

cond-mat.mtrl-sci↗

arXiv2026

Effect of front surface engineering on high energy electron, X-ray and heavy ion generation from Relativistic laser interaction with thick high-Z targets

Relativistic lasers on solid targets generate hot electrons, and other secondary particles. These particles can be used for radiography, cancer therapy, or isochoric heating. A lower density or structured coating on high-Z targets can improve laser-target energy coupling and subsequently enhance overall particle emission. In this work performed at the Scarlet Facility, a $10^{21}$ W/cm$^2$ intense pulse was incident on front surface coatings on 1 mm thick Ta. These coatings include a 12 $μ$m plastic coating, a 50 $μ$m thick foam coating, and a Au nanowire (NW) coating. Post-damage craters are correlated with reflected light on a MACOR screen, illustrating that less absorption in a target is directly tied to smaller craters. Additionally, more absorption in a target also leads to more MeV electrons and X-rays. Bare targets performed the best for electron and MeV X-ray generation, with X-rays of 30 MeV detected, as coatings tested were too thick and thus experienced lower intensities. Due to this larger spot size, foam and NW-coated targets generated the greatest heavy ion acceleration. Particle-in-cell simulations tested on bare and plastic-coated targets illustrate that $\sim μ$m thick plastic coatings perform better than bare Ta. These results underline the importance of density and thickness control of coatings on high-Z materials. In the future, post-damage crater analysis could provide an easy way to benchmark absorption in a sample, and could later be compared against absorption estimates from particle-in-cell simulations.

physics.plasm-ph↗