Plasmas created by the interaction of high power optical laser with a target surface can be used as a source of soft X-ray lasers. Plasma and pump laser characteristics play significant role in achieving high gain coefficient for such plasma based on soft X-ray lasers. In the present work, the plasma active medium parameters for germanium element at a wavelength of 19.6 nm irradiated by a double-pulse pump laser have been studied using MED103 hydrodynamic code. For this purpose, first, the effects of laser intensity, pulse width and delay time of two pulses on the gain coefficient have been investigated and the optimum conditions for the maximum gain extent of Ne-like germanium soft X-ray laser are obtained. Then, in order to calculate the intensity of such high gain lasers in which Linford equation is invalid, we have adopted the general formula of amplified spontaneous emission intensity, which is valid in all range of intensities even at much higher intensities than saturation intensity. Finally, the soft X-ray laser intensities in the saturated areas for different plasma lengths have been calculated. The results show that the output of soft X-ray laser intensity with 294 cm⁻¹ gain coefficient can reach to about several times saturated intensity by applying a 1–2 mm plasma length as the active medium.

中文翻译：

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类Ne软X射线激光器中等离子体活性介质和增益饱和区的参数研究

高功率光学激光与目标表面相互作用产生的等离子体可用作软 X 射线激光源。等离子体和泵浦激光器的特性在实现这种基于软 X 射线激光器的等离子体的高增益系数方面起着重要作用。在目前的工作中，使用MED103流体动力学代码研究了双脉冲泵浦激光器在19.6 nm波长处辐照锗元素的等离子体活性介质参数。为此，首先研究了激光强度、脉冲宽度和两个脉冲的延迟时间对增益系数的影响，得到了类氖锗软X射线激光器最大增益范围的最佳条件。然后，为了计算Linford方程无效的这种高增益激光器的强度，我们采用了放大自发辐射强度的一般公式，该公式在所有强度范围内都有效，即使强度远高于饱和强度。最后，计算了不同等离子体长度下饱和区域的软 X 射线激光强度。结果表明，输出软X射线激光强度为294 cm通过应用 1-2 mm 的等离子体长度作为活性介质，^-1增益系数可以达到大约数倍的饱和强度。