Numerical modeling of frequency conversion of high-intensity laser pulses into XUV/X and THz radiation

近年来，在科学研究和实际应用中都有很大兴趣的以前未使用的频率范围内开发强大的相干辐射源的研究工作一直在进行。其中两个频率范围是XUV/X和THz频率。由于其高频率，XUV/X辐射在原子和分子光谱，等离子体表征和原子科学中有重要的应用，并在生命和材料科学的显微镜应用中有新的应用前景。在可见光谱的低频端，太赫兹辐射在远程化学和结构完整性分析以及安全领域具有重要的应用前景。XUV/X和太赫兹辐射之间的共同点是，两者都可以由高强度飞秒激光脉冲和低密度介质（气体或等离子体）相互作用产生。目前XUV/X和太赫兹产生的主要挑战是增加源的产量，并且在XUV/X的情况下，尽可能地向高频（X射线范围）扩展频谱，以便获得足够的强度来实现设想的应用。本研究计划的总体目标是从理论上研究高强度激光脉冲在低密度介质中的频率转换过程，重点研究XUV/X和太赫兹辐射的产生。在这个研究项目中开发的建模工具将允许：(i)提高我们对物理过程的总体理解，（ii）优化实验设置，以及（iii）通过数值模拟研究新的更复杂的实验安排，以增加感兴趣频率范围内的产量。这些计算机工具将成为“建模工具箱”的关键组成部分，将来可以应用于与高强度激光脉冲和低密度介质之间相互作用有关的许多其他问题。

In recent years there has been an intense research effort to develop powerful and coherent radiation sources in previously unused frequency ranges of great interest both for scientific research and practical applications. Two of these frequency ranges are the XUV/X and THz frequencies. Due to its high frequency, XUV/X radiation finds its important applications in atomic and molecular spectroscopy, characterization of plasmas, and in attoscience, and promises new applications in the context of microscopy applied to life and materials sciences. At the low-frequency end of the visible spectrum, the THz radiation promises important applications in the areas of remote chemical and structural integrity analysis, and in security. A common point between XUV/X and THz radiation is that both can be generated from the interaction of a high-intensity femtosecond laser pulse and a low density medium - gas or plasma. The main current challenge in both XUV/X and THz generation is to increase the yield of the sources and, in the case of XUV/X, extend the spectrum as far as possible towards high frequencies (X-ray range), in order to obtain sufficient intensities to achieve the envisaged applications. The general goal of this research program is to investigate theoretically the frequency conversion process of high intensity laser pulses in low density media, with emphasis on the generation of XUV/X and THz radiation. The modeling tools that will be developed within this research program will allow to: (i) improve our general understanding of the physical processes, (ii) optimize the experimental setups, and (iii) investigate through numerical simulations new more sophisticated experimental arrangements to increase the yield in the frequency ranges of interest. These computer tools will be key components of a "modeling toolbox" that can be applied in the future to many other problems related to the interaction between high-intensity laser pulses and low-density media.