X-ray generation from gas-puff jets irradiated by UNR Leopard laser

The development of efficient x-ray probes with photon energies 1–20 keV became important for high-energy density physics (HEDP) research at larger scale facilities such as OMEGA and NIF. The goal of our studies is better understanding of the mechanisms of the laser energy to x-ray conversion efficiency (both thermal and non-thermal) and the directionality of x-rays. Experiments were performed at the UNR Leopard laser operated with 350 fs or 0.8 ns pulses. The supersonic linear nozzle (generated Ar clusters/monomer mixture with density up to 2 × 10
¹⁹
cm
⁻³
) was compared to the cylindrical tube sub-sonic nozzle. The linear (elongated) cluster/gas jet is more uniform than the cylindrical one in experiments with the laser beam orthogonal to the jet axis. Additionally, the elongated jet provides capability to study laser beam self-focusing (when laser beam propagates along a jet plane) and plasma channel formation that are interconnecting with efficient x-ray generation. The laser radiation flux density in the focal spot was up to 2 × 10
¹⁹
W/cm
²
(fs pulse). Diagnostics included x-ray diodes, pinhole cameras and spectrometers. Signatures of x-ray emission from linear and tube nozzles were found to be very different. It was observed that emission in the 1–55 keV region was strongly anisotropic depending on the direction of laser beam polarization for fs laser pulse and supersonic linear nozzle. Energy radiated in the 1–3 keV region by a linear nozzle was an order of magnitude higher than from a tube nozzle. Non-LTE models have been implemented to analyze the spectroscopic data. It was shown that plasma from the linear nozzle was by an order of magnitude hotter than one from the tube nozzle. Evidence of electron beam generation in jets' plasma was found. Observed effects are explained by presence of Ar clusters in the jet from the linear nozzle. Future research will focus on study of cluster formation in different linear nozzles with Ar and mixture of Ar/Kr jets with varying of its parameters for optimization x-ray yield and power.