强飞秒激光脉冲在复杂气体环境中的传输研究

The intensefemtosecond laser pulse will interact with the matters in the gas as it propagates in the gas, thereby generating nonlinear phenomena like the supercontinuum generation, THz emission, high-order harmonic generation and so on. And these phenomena can find important application prospects in the field of astronomy, meteorology as well as national defense etc., thus becoming one of the hot topics in the field of the interaction between the intense laser pulses and materials. In this project, we will investigate the propagation of the intense femtosecond laser pulse in the complex gaseous environment where the pressure, temperature, humidity are different and various inclusions are included through the combination of numerical and experimental methods. Theoretically, we numerically solve the time-dependent Schr?dinger equation which describes the behavior of single atom (molecule) under the action of intense laser field utilizing the programs that we have already used to study the strong filed physics, and connect the laser propagation which is a macroscopic phenomenon with interaction between atom (molecule) and laser pulses which is a microscopic process through the statistical ensemble, so as to explore the essence of high-order Kerr effects, calculate the high-order Kerr indices and complete the propagation model. Experimentally, we model the complex gaseous environments through the cavity of the interaction between laser and gas, measure the high-order Kerr indices and carry out the needed experiments in the cavity when numerically solving the propagation equation in the corresponding environment, so as to investigate the propagation law of intense femtosecon laser pulse in complex gaseous environments. It is in the hope of obtaining the effective measures to control the propagation of laser pulse as well as filamentation, and lay a foundation for the long range propagation of intense femtosecond laser pulse in the complex atmospheric environment.

飞秒激光脉冲在气体中传播会与其中的物质发生相互作用产生诸如超连续谱发射、太赫兹辐射、高次谐波发射等非线性现象。这些效应在天文、气象、国防等领域有着重要应用前景，是激光与物质相互作用领域的焦点课题之一。在本项目中，我们将结合数值和实验研究强飞秒激光脉冲在不同压强、温度、湿度、以及掺入杂质等复杂气体环境下的传输。理论上利用已有研究强场物理的程序数值求解单个原子(分子)在激光场作用下的含时薛定谔方程，通过统计系综将激光传播这一宏观现象同原子(分子)与激光相互作用的微观过程联系起来，以探求高阶克尔效应本质，计算高阶克尔系数，完善传播模型。实验上通过激光与气体相互作用腔体模拟各种复杂气体环境，测定高阶克尔系数，数值求解相应环境下的传播方程的同时在腔体中进行相关实验，研究复杂气体环境下飞秒激光脉冲的传播规律。以期获得控制激光传播及成丝的有效途径，为实现飞秒激光脉冲在复杂气体环境下的远距离传输奠定基础。

飞秒激光脉冲在空气中传播时，当克尔自聚焦效应与等离子散焦效应达到动态平衡之后会形成稳定的等离子体通道，这一过程又被称为成丝。飞秒激光成丝过程中伴随着光电离、超连续谱产生、太赫兹辐射、高次谐波发射、锥角辐射和荧光发射等非线性现象。研究这些现象，不仅在弄清超短激光脉冲与原子、分子相互作用机理以及激光脉冲在不同介质环境中的传输规律等方面具有重要的学术价值，而且在天文、气象以及国防等领域都具有重要的应用前景，如远程探测、诱导闪电、人工降雨、空气波导等。这些诱人的应用使飞秒激光成丝成为了近年来的研究热点，人们在理论、实验和应用方面进行了深入的研究，并获得了大量重要的结果。.而这些应用的基础，则是解决强激光脉冲在不同压强、温度、湿度及掺杂物等各种气体环境下的传输问题。在本项目中，我们研究了强飞秒激光脉冲在不同压强、温度、湿度以及掺入杂质等复杂气体环境下的传输，并对传输过程中的、超连续谱、锥角辐射和荧光等光发射进行了系统的研究, 例如首次在实验上观测到了持续时间长达50 μs的光发射现象。通过激光与气体相互作用腔体模拟各种复杂气体环境，研究复杂气体环境下飞秒激光脉冲的传播规律，例如我们发现在脉冲能量相同的情况下，整形脉冲产生的等离子体通道比变换极限脉冲长了很多。获得了控制激光传播及成丝的有效途径，为实现飞秒激光脉冲在复杂气体环境下的远距离传输奠定基础。