arXiv subjects

Uddhab Chaulagain

Publications and source records attributed to Uddhab Chaulagain.

4 recordsLinked to original sources

arXiv2026

Calibration of scintillator-based X-ray detectors for broadband laser-driven X-ray radiation

Laser-driven X-ray sources produce broadband radiation with substantial shot-to-shot fluctuations, requiring calibrated detector-response models for quantitative measurements of photon fluence and spectral distribution. Scintillator-based flat-panel detectors, originally developed primarily for medical and industrial X-ray imaging, are increasingly being adopted for diagnostics of laser-plasma-based X-ray sources because they provide large-area, spatially resolved detection. We report the calibration of two complementary X-ray detector systems: a CsI:Tl-based flat-panel detector and a plastic-scintillator filter-stack spectrometer intended for spectral reconstruction. Both detectors were characterized using well-defined ISO 4037 N-series reference radiation qualities, providing controlled polychromatic X-ray fields for establishing their signal response and signal-to-fluence conversion.

physics.optics↗

arXiv2024

Bright coherent attosecond X-ray pulses from beam-driven relativistic mirrors

Bright ultrashort X-ray pulses allow scientists to observe ultrafast motion of atoms and molecules. Coherent light sources, such as the X-ray free electron laser (XFEL), enable remarkable discoveries in cell biology, protein crystallography, chemistry or materials science. However, in contrast to optical lasers, lack of X-ray mirrors demands XFELs to amplify radiation over a single pass, requiring tens or hundreds of meters long undulators to produce bright femtosecond X-ray pulses. Here, we propose a new ultrafast coherent light source based on laser reflection from a relativistic mirror driven by a relativistic charged particle beam in micrometer-scale plasma. We show that reflection of millijoule-level laser pulses from such mirrors can produce bright, coherent and bandwidth-tunable attosecond X-ray pulses with peak intensity and spectral brightness comparable to XFELs. In addition, we find that beam-driven relativistic mirrors are highly robust, with laser-induced damage threshold exceeding solid-state components by at least two orders of magnitude. Our results promise a new way for bright coherent attosecond X-ray pulse generation, suitable for unique applications in fundamental physics, biology and chemistry.

physics.plasm-ph↗

arXiv2023

Anomalous Relativistic Emission from Self-Modulated Plasma Mirrors

The interaction of intense laser pulses with plasma mirrors has demonstrated the ability to generate high-order harmonics, producing a bright source of extreme ultraviolet (XUV) radiation and attosecond pulses. Here, we report an unexpected transition in this process. We show that the loss of spatio-temporal coherence in the reflected high-harmonics can lead to a new regime of highly-efficient coherent XUV generation, with an extraordinary property where the radiation is directionally anomalous, propagating parallel to the mirror surface. With analytical calculations and numerical particle-in-cell simulations, we discover that the radiation emission is due to laser-driven oscillations of relativistic electron nanobunches which originate from a plasma surface instability induced by collisionless absorption of the laser.

physics.plasm-ph↗

arXiv2021

First radiative shock experiments on the SG-II laser

We report on the design and first results from experiments looking at the formation of radiative shocks on the Shenguang-II (SG-II) laser at the Shanghai Institute of Optics and Fine Mechanics in China. Laser-heating of a two-layer CH/CH-Br foil drives a $\sim$40 km/s shock inside a gas-cell filled with argon at an initial pressure of 1 bar. The use of gas-cell targets with large (several mm) lateral and axial extent allows the shock to propagate freely without any wall interactions, and permits a large field of view to image single and colliding counter-propagating shocks with time resolved, point-projection X-ray backlighting ($\sim20$ $μ$m source size, 4.3 keV photon energy). Single shocks were imaged up to 100 ns after the onset of the laser drive allowing to probe the growth of spatial non-uniformities in the shock apex. These results are compared with experiments looking at counter-propagating shocks, showing a symmetric drive which leads to a collision and stagnation from $\sim$40 ns onward. We present a preliminary comparison with numerical simulations with the radiation hydrodynamics code ARWEN, which provides expected plasma parameters for the design of future experiments in this facility.

physics.plasm-ph↗