Angular distribution and conversion of multi-keV L-shell X-ray sources produced from nanosecond laser irradiated thick-foil targets

Abstract

An experimental study on the angular distribution and conversion of multi-keV X-ray sources produced from 2 ns-duration 527nm laser irradiated thick-foil targets on Shenguang II laser facility (SG-II) is reported. The angular distributions measured in front of the targets can be fitted with the function of f(u) ¼ aþ (12a)cos b u (u is the viewing angle relative to the target normal), where a ¼ 0.41 + 0.014, b ¼ 0.77 + 0.04 for Ti K-shell X-ray sources (4.75 keV for Ti K-shell), and a ¼ 0.085 + 0.06, b ¼ 0.59 + 0.07 for Ag/Pd/Mo L-shell X-ray sources (2-2.8 keV for Mo L-shell, 2.8-3.5 keV for Pd L-shell, and 3-3.8 keV for Ag L-shell). The isotropy of the angular distribution of L-shell emission is worse than that of the K-shell emission at larger viewing angle (.708), due to its larger optical depth (stronger self-absorption) in the cold plasma side lobe surrounding the central emission region, and in the central hot plasma region (emission region). There is no observable difference in the angular distributions of the L-shell X-ray emission among Ag, Pd, and Mo. The conversion efficiency of Ag/Pd/Mo L-shell X-ray sources is higher than that of the Ti K-shell X-ray sources, but the gain relative to the K-shell emission is not as high as that by using short pulse lasers. The conversion efficiency of the L-shell X-ray sources decreases with increasing atomic numbers (or X-ray photon energy), similar to the behavior of the K-shell X-ray source.

Simulations of high power laser-produced multi-keV X-ray source

“…The simulation results agree well with the analysis scaling-law (x-ray brightness proportional to Te*Ne 2 ) [8,9] . In formula (2), the target self-absorption is not included because the plasma is supposed to be optically thin for the Ti K-shell x-ray.…”

“…The experiment performed on Shen-Guang II laser facility proposed that 2µm thin target can produce 50% greater x-ray source brightness than 6µm thick target, and the Ultra-thin target with thickness 1.6µm will decrease x-ray source brightness [8,9] , agreeing with the simulations well. target thickness 1pm * 0.5pm Figure 6 x-ray emission intensity versus of target thickness…”

“…Most of the articles concerning this issue have concentrated on the influence of the laser intensity [1][2][3][4][5] , and optimization was made to produce higher brightness x-ray source at lower laser driven. At the same time, some novel techniques such as thin foil target and shaped laser pulse have been proposed to increase the x-ray brightness [6][7][8][9] . To obtain a deep vision in these works, detailed hydrodynamic simulations and atomic physics calculations of the x-ray emission are important.…”

Production of photoionized plasmas in the laboratory with x-ray line radiation

“…Using the efficiency of L-shell emission, we can estimate ξ. Our model accounts for the profile of the X-ray focal spot (fitted to a super-Gaussian) and assumes a cos(q) 1/2 variation in X-ray emission [15]. This allowed us to model the emission as a function of the distance in the direction normal to the focal spot, and also in the direction parallel to the focal spot plane.…”

Diagnostic development in precise opacity measurement of radiatively heated Al plasma on Shenguang II laser facility

“…18 Recently the additional ͑ninth͒ laser beam, which can also deliver 70-150 ps short pulse besides the nanosecond long pulse, was established on the Shenguang II laser facility. [19][20][21] The ninth laser beam could be used to generate shorter backlighter compared with the previous experiments. 7,[14][15][16][17] The shorter backlighter could provide better temporal resolution.…”