The effects of ASE contrast and beams mutual alignment on the gamma-ray yield in laser-plasma interactions with artificial prepulseстатья
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Дата последнего поиска статьи во внешних источниках: 4 июня 2021 г.
Аннотация:We present experimental study of the bremsstrahlung gamma-rays generation in a plasma interacting with 50 fs laser pulse in slightly relativistic regime (intensity ~2*10^18 W/cm^2). A pre-plasma layer on the surface of the molybdenum target is formed by an additional laser pulse with a duration of 8 ns and an intensity of ~2*10^12 W/cm^2. The energy and intensity of the artificial pre-pulse exceed those of the amplified spontaneous emission (ASE) pedestal of the main pulse by ~10^3 and 10 times (for contrast 10^-7), respectively. It was shown that the low ASE contrast (>10^-7) is the crucial condition for increasing (in comparison to the case without artificial pre-pulse) of the integral gamma-rays yield when the nanosecond pulse is ahead of the femtosecond one by >20 ns. Interferometry data show that the reason of the gamma-rays yield increasing is a pre-plasma layer initially produced by artificial pre-pulse and re-created by the ASE. The optimum conditions for gamma-rays yield achieved if (i) the pre-pulse comes ~25 ns in advance, (ii) ASE contrast is 10^-7 and lower and (iii) the femtosecond focal point is shifted by ~100 mkm from the center of the nanosecond pre-pulse focal spot and by ~100 mkm above the target surface.