光修饰类氢等离子体C5 + X射线laser在“水窗”区产生阿秒脉冲
Attosecond pulse formation in the "water window" range by optically dressed hydrogen-like plasma-based C5+ X-ray laser
摘要：
本文给出了在“水窗”范围内，类氢C5+等离子体基X射线激光器通过激活介质的光调制形成阿秒脉冲的解析理论，并考虑了上激光态辐射衰变引起的粒子数反转的变化。本文导出了强激光场同时作用于具有含时粒子数反转的X射线激光放大的X射线场的解析解，并利用它找到了窄带籽晶X射线场产生阿秒脉冲的最佳条件。我们表明，脉冲的形状可以得到改善的脉冲峰值强度降低的成本（i）通过外部衰减的放大X射线场的共振谱分量或（ii）通过使用共振吸收介质（活性介质的X射线激光器后的粒子数反转的符号的变化）的脉冲形成。理论分析的结果与Maxwell-Bloch方程的数值解吻合得很好，后者考虑了激活介质的非线性和放大的自发发射。通过理论分析和数值计算，我们证明了在“水窗”范围内，在载波波长3.4 nm处产生持续时间小于200 W、峰值强度超过10^12 W/cm ^2的阿秒脉冲训练的可能性，这使得它们在生物学和医学应用中具有吸引力。
英文摘要：
In this paper, we present the analytical theory of attosecond pulse formation via optical modulation of an active medium of the hydrogen-like C5+ plasma-based X-ray laser at 3.4 nm wavelength in the "water window" range, taking into account a variation of the population inversion caused by radiative decay of the upper lasing states. We derive an analytical solution for the X-ray field amplified by an X-ray laser with time-dependent population inversion, which is simultaneously irradiated by a strong optical laser field, and use it to find the optimal conditions for the attosecond pulse formation from a narrowband seeding X-ray field. We show that the shape of pulses can be improved at the cost of reduced pulse peak intensity (i) via external attenuation of the resonant spectral component of the amplified X-ray field or (ii) by using a resonantly absorbing medium (the active medium of the X-ray laser after the change of sign of the population inversion) for the pulse formation. The results of the analytical theory are in a good agreement with the numerical solutions of the Maxwell-Bloch equations which account for the nonlinearity, as well as the amplified spontaneous emission, of the active medium. Both analytically and numerically we show the possibility to produce a train of attosecond pulses with sub-200 as duration and the peak intensity exceeding 10^12 W/cm^2 at the carrier wavelength 3.4 nm in the "water window" range, which makes them attractive for the biological and medical applications.
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