氖原子对2000 eV X射线激光透明的产生机制

X射线自由电子激光与物质相互作用时出现了X射线透明现象,研究X射线透明现象的产生机制对理解X射线自由电子激光与物质相互作用过程具有重要参考价值.本文基于FAC(Flexible Atomic Code)程序计算的氖原子(离子)对2000 eV X射线的光电离截面和俄歇衰变速率,确定了不同通量密度下氖原子的主要电离方式;通过建立和解速率方程,得到了确定的电离方式中氖元素各电子组态数目比例随时间变化的公式,计算了氖原子在通量密度为2000和10000?~(-2)·fs~(-1)、持续时间为20 fs、光子能量为2000 eV的X射线激光照射下,任意时刻各主要电子组态的原子数目比例和总的氖原子平均光电离截面.建立了价电子完整的空心原子的数目比例随通量密度和曝光时间变化的公式.发现裸核和空心原子都会导致X射线透明,且选择恰当的通量密度和脉冲持续时间可以使价电子完整的空心原子数目比例达到极高.

2000 eV X-ray laser transparent mechanism of neon atom

X-ray transparency occurs during the interaction of X-ray free electron laser with matter. The study of the mechanism of X-ray transparency is of great value for understanding the interaction between X-ray free electron laser and matter. In this paper, the main ionization modes from neutral neon atom till bare nucleus at different flux densities are determined based on the 2000 eV photoionization cross sections and the Auger decay rates of various neon atoms (ions), calculated by the Flexible Atomic Code program. By establishing and solving the rate equations, the formulas of the proportions of various electronic configurations of neon in the main ionization mode are obtained. The proportions of electron configurations in the main ionization modes and the atomic average photoionization cross sections at flux densities of 2000 and 10000 Å^-2·fs^-1 are calculated by using the formulas. The ratios of the number of hollow atoms to that of complete valence electrons at any time under different flux density laser irradiations are calculated. It is found that both the bare nuclei and the hollow atoms cause X-ray transparency, and a relatively high ratio of the number of hollow atoms to that of complete valence electrons can be achieved by choosing appropriate flux density and pulse duration.