强场隧穿电离诱导产生的振动态分辨的空气激光研究

The development of ultrafast and intense laser sources has opened a route to study laser-matter interaction in unexplored extreme nonlinear regime. As one of the most fundamental and important quantum processes, tunnel ionization is a hot research area in strong laser field physics. In recent years, air laser induced by tunnel ionization in intense laser fields has attracted considerable attention not only because of its potential applications in remote atmospheric sensing but also because it provides us a brand new approach to investigate the highly nonlinear phenomena in strong laser field. The generation of air lasers inherently contents the information of ultrafast laser excitation. Besides, the ultrafast dynamics of molecular rotations and vibrations can encode their characteristics into the air laser, which can be measured in frequency domain or in time domain. In this research project, we will carry out the correlated measurement of air lasers and the corresponding fluorescence based on pump-probe scheme. The vibration-resolved spectra with time-varying information will be used to reveal the physical mechanisms behind the abnormal dependence of air laser on polarization ellipticity of the driving field. Meanwhile, this project aims at dynamically controlling the population of molecular vibrational states and exploring a new method to investigate ultrafast processes of molecule ions with the help vibration-resolved fluorescence.

超强超快激光技术的发展推动激光与物质相互作用步入高度非线性范畴，隧穿电离作为其中最基础又最重要的量子过程之一，是强场激光物理研究的重要方向。近年来飞秒激光隧穿电离诱导产生的自由空气激光被实验发现，由此带来的一系列崭新的物理图像和技术进展引起国内外的广泛关注。空气激光不仅为远程大气遥感等重要应用提供了一种全新的可能实现途径，而且有望成为强场激光物理研究的有效手段。空气激光的产生包含着超快光场电离、分子激发等一系列物理过程，因此解码空气激光的频域及时域信息是获取强场中分子激发、转动、振动等重要超快动力学信息的有效途径。项目在本研究小组以往工作的基础上，拟采用泵浦-探测方法关联测量振动分辨的空气激光和对应荧光的光谱信息与动态演化过程，对比研究振动能级的超快动力学演化，揭示空气激光超快光激发背后的物理机制，实现分子振动能级布居的动态操控，探索发展振动态分辨的超快动力学研究方法。

超强飞秒激光作为泵浦、飞秒光丝作为载体，基于强场隧穿电离诱导产生的氮分子离子空气激光一经发现就迅速引起了国内外广泛关注，为实现高灵敏度的远程大气遥感提供了一个重要实现手段，是远程遥感的理想光源之一。本项目围绕强场隧穿电离诱导产生的空气激光这一主题进行研究，具体针对澄清空气激光产生机理、空气激光系统超快动力学追踪、远程操控空气激光三方面展开深入研究，有助于推动氮气离子空气激光理论的完善，拓宽氮气离子空气激光的应用前景。获得的研究成果如下：.1、实验上探索氮气的隧穿电离特性，证实内层轨道电离的贡献，理论上采用密度矩阵理论建立了一个研究强场中离子超快动力学的电离耦合模型，实现了亚周期时间内离子的量子相干控制，证明氮分子离子空气激光中存在粒子数反转的条件和机制。.2、追踪空气分子激发态的超快动力学过程，获取激发态分子的寿命、退激发态过程、非线性性质等信息。.3、采用椭圆偏振整形的超快激光场，有效增加氮分子离子激光的粒子反转布局数，极大提高空气激光亮度。