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

近年来，人们进行了大量的研究工作，以开发以前未使用的频率范围内的强大和相干辐射源，这对科学研究和实际应用都很有意义。其中两个频率范围是XUV/X和THz频率。由于其频率高，XUV/X辐射在原子和分子光谱学、等离子体表征和物理学中得到了重要的应用，并有望在显微技术应用于生命和材料科学的背景下获得新的应用。在可见光谱的低频端，太赫兹辐射有望在远程化学和结构完整性分析以及安全领域得到重要应用。XUV/X和THz辐射的一个共同点是，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。XUV/X和THz产生的当前主要挑战是增加源的产额，在XUV/X的情况下，尽可能将光谱扩展到高频(X射线范围)，以便获得足够的强度来实现设想的应用。这项研究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，重点是XUV/X辐射和THz辐射的产生。在本研究计划中开发的建模工具将允许：(I)提高我们对物理过程的一般理解，(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，以增加感兴趣的频率范围内的产量。这些计算机工具将是未来可应用于高强度激光脉冲与低密度介质之间相互作用的许多其他问题的“建模工具箱”的关键组件。

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.