In this work, we optimized a clean, versatile, compact source of soft X-ray radiation $(E_{\text{x}\text{-}\text{ray}}\sim 3~\text{keV})$ with an yield per shot up to $7\times 10^{11}~\text{photons}/\text{shot}$ in a plasma generated by the interaction of high-contrast femtosecond laser pulses of relativistic intensity $(I_{\text{las}}\sim 10^{18}{-}10^{19}~\text{W}/\text{cm}^{2})$ with supersonic argon gas jets. Using high-resolution X-ray spectroscopy approaches, the dependence of main characteristics (temperature, density and ionization composition) and the emission efficiency of the X-ray source on laser pulse parameters and properties of the gas medium was studied. The optimal conditions, when the X-ray photon yield reached a maximum value, have been found when the argon plasma has an electron temperature of $T_{\text{e}}\sim 185~\text{eV}$ , an electron density of $N_{\text{e}}\sim 7\times 10^{20}~\text{cm}^{-3}$ and an average charge of $Z\sim 14$ . In such a plasma, a coefficient of conversion to soft X-ray radiation with energies $E_{\text{x}\text{-}\text{ray}}\sim 3.1\;(\pm 0.2)~\text{keV}$ reaches $8.57\times 10^{-5}$ , and no processes leading to the acceleration of electrons to MeV energies occur. It was found that the efficiency of the X-ray emission of this plasma source is mainly determined by the focusing geometry. We confirmed experimentally that the angular distribution of the X-ray radiation is isotropic, and its intensity linearly depends on the energy of the laser pulse, which was varied in the range of 50–280 mJ. We also found that the yield of X-ray photons can be notably increased by, for example, choosing the optimal laser pulse duration and the inlet pressure of the gas jet.

中文翻译：

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由相对论强度的高对比度飞秒激光脉冲在超音速 Ar 气体射流中形成的清洁软 X 射线辐射源

在这项工作中，我们优化了一种清洁、多功能、紧凑的软 X 射线辐射源 $(E_{\text{x}\text{-}\text{ray}}\sim 3~\text{keV})$ 每次射击的产量高达 $7\times 10^{11}~\text{photons}/\text{shot}$ 在由相对论强度的高对比度飞秒激光脉冲相互作用产生的等离子体中 $(I_{\text{las}}\sim 10^{18}{-}10^{19}~\text{W}/\text{cm}^{2})$ 用超音速氩气喷射。利用高分辨率 X 射线光谱学方法，研究了 X 射线源的主要特性（温度、密度和电离成分）和发射效率对激光脉冲参数和气体介质性质的依赖性。当氩等离子体的电子温度为 $T_{\text{e}}\sim 185~\text{eV}$ ，电子密度为 $N_{\text{e}}\sim 7\times 10^{20}~\text{cm}^{-3}$ 和平均收费 $Z\sim 14$ . 在这样的等离子体中，转换为具有能量的软 X 射线辐射的系数 $E_{\text{x}\text{-}\text{ray}}\sim 3.1\;(\pm 0.2)~\text{keV}$ 达到 $8.57\乘以 10^{-5}$ ，并且不会发生导致电子加速到 MeV 能量的过程。发现该等离子体源的 X 射线发射效率主要取决于聚焦几何形状。我们通过实验证实 X 射线辐射的角分布是各向同性的，其强度线性取决于激光脉冲的能量，其变化范围为 50-280 mJ。我们还发现，通过选择最佳的激光脉冲持续时间和气体射流的入口压力，可以显着提高 X 射线光子的产量。