气相介质中二维电子光谱的实验研究

Two-dimensional (2D) electronic spectroscopy has been used to explicitly trace the electronic dynamics with femtosecond accuracy, which provides a novel, attractive ultrafast spectral method over the past decade. In the proposal, passively phase-stable 2D electronic spectroscopy based on a four-quadrant mirror is designed and developed. The new design, which is particularly simple and robust, achieves subwavelength stability without the need for active stabilization. Since only reflective optical components are used, the setup is suitable for few-cycle laser pulses and ultrabroad-bandwidth light in the ultraviolet, visible and near-IR region, which will provide a versatile tool for chemical physics, material science, biophysics and other interdisciplines. Moreover, in the proposal, the 2D spectroscopy is creatively extended from condensed-phase to gas-phase medium, from perturbative nonlinear optics to nonperturbative nonlinear optics, and from resonance to off-resonance absorption. The 2D spectroscopy in gas-phase will been applied to observe the temporal evolution of highly-excited electron (or free electron) wave-packet, allowing to investigate the ultrafast processes including electronic relaxation, quantum beats and coherent dephasing with femtosecond accuracy. The new spectral method will provide a new perspective into electronic dynamics in atomic and molecular physics and strong-field nonlinear optics.

二维电子光谱可以实现对电子量子态时域演化的精密观测，是近年来一种新兴的超快激光光谱学方法。本项目拟设计发展基于"四象限分束镜"的被动相位自稳定二维电子光谱系统。这种新设计光谱系统相比同类实验系统，具有简单灵活、亚波长量级高稳定性。新仪器设计全部由反射光学元件构成，非常适合应用于少数周期超短脉冲，并且从紫外到近红外区域超宽带可调，为物理化学、材料科学、生物物理等学科领域提供了可靠的实验技术手段。本项目还将更近一步、创新性的将二维光谱方法从凝聚态物质拓展到气相物质，从微扰非线性光学拓展到非微扰非线性光学，从共振吸收到非共振吸收，观察气相原子分子中高激发态（或电离态）的电子超快动力学过程，在飞秒时间尺度研究高激发态电子的弛豫过程、量子拍频和相干失相等过程。新的光谱学方法为深入研究原子分子动力学和强场非线性光学开拓了全新的视角。

二维傅里叶变换光谱为我们提供了强大的科学工具，研究激发波长和发射波长之间的关联，二维光谱提供了比一维光谱更多的光谱信息，使我们从更新的角度分析复杂系统光诱导化学反应中的超快动力学行为。这种光谱方法已经成功的应用于分析光合作用系统和半导体纳米结构的超快动力学行为。本项目发展了自相位稳定的二维电子光谱，可以在超宽带的频谱范围内调谐。我们提出了新的方法确定二维光谱激发脉冲序列的决定零点，用于避免二维光谱实验结果中相位失真问题。发展了二维光谱的相位重构算法，修正了由于零点错误所带来的相位失真。新的相位重构方法可以和常用的二维光谱投影(projection-slice theorem)一起使用，提高二维光谱实验结果的可信度。我们发现了液相介质中的高阶非线性效应，可以用来观察液相介质中的振动弛豫和电子弛豫。总结极紫外波长泵浦探测实验的最新实验结果，用来观察分子解离和异构化的过程，发现分子离子中分子态的共振激发在解离中的重要作用。发展了高功率太赫兹脉冲光源，为进一步超快动力学研究提供可靠光源。