整形飞秒光场控制成丝诱导分子荧光发射的研究

The characteristic molecular fluorescence induced by femtosecond laser filamentation can find important application prospect in the remote sense of trace amount of chemical biological radicals and pollutants in atmospheric environment. However, the low intensity of filament-induced fluorescence restrains its practical applications. In this project, we attempt to utilize the shaped femtosecond laser field to control the filament-induced molecular fluorescence emission, aiming at enhancing the fluorescence emission. By measuring fluorescence spectrum emitted during the filamentation of shaped femtosecond pulse, we attempt to study influence of the temporally, spatially, and polarization shaped femtosecond laser field on the filament-induced molecular fluorescence emission. Through the time-resolved measurements of fluorescence emission, we try to investigate the influence of these shaped femtosecond fields on the molecular alignment, rotational revival, population trapping, impact excitation and other dynamical processes that occur during the filament-induced molecular fluorescence emission, thus further understanding the emission mechanism of filament-induced molecular fluorescence. Based on the above study and in combination with the advantages of these pulse shaping techniques, we attempt to specifically control the dynamical processes that affect the molecular fluorescence emission, and the competition relationship between these processes, so as to explore the effective ways to enhance filament-induced molecular fluorescence emission, thereby laying a foundation to conduct the remote detection via filament-induced molecular fluorescence technology.

飞秒激光脉冲成丝过程中诱导分子产生的特征荧光在远程探测大气环境中微量的化学、生物基团和污染物等方面有着重要的应用前景。不过，成丝诱导分子荧光的强度很低，不利于其实际应用。在本项目中，我们拟利用整形飞秒光场控制成丝诱导分子荧光发射，以期达到增强荧光发射的目的。通过测定整形的飞秒脉冲成丝过程中产生的荧光光谱，研究时域、空间和偏振整形的飞秒光场对成丝诱导分子荧光发射的影响；通过对荧光发射的时间分辨测量，研究各种整形飞秒光场对成丝诱导分子荧光发射过程中发生的分子准直、转动重建、布居捕获、碰撞激发、直接电离等效应的影响，深入了解成丝诱导分子荧光的发射机制。在此基础上结合各种脉冲整形技术的优势有针对性地控制影响分子荧光发射的动力学过程以及这些过程之间的竞争关系，探索增强成丝诱导分子荧光发射的有效途径，为利用成丝诱导分子荧光技术开展远程探测奠定基础。

飞秒激光成丝诱导分子技术具有很高的空间（几十微米）和时间（皮秒量级）分辨能力，而且能同时实现对介质中(例如，空气，水)多种成分的探测，使其在远程探测大气环境中微量的化学、生物基团和污染物等方面有着重要的应用前景，为实时、高效、精准地监测大气环境提供了极好的平台。激光的波长、振幅、相位、空间分布、时间分布等参数不仅会影响飞秒激光所成丝的长度、寿命和形态，还会影响丝中分子的准直、激发、电离、解离等动力学过程，从而影响分子荧光的发射。此外，温度、湿度、气压、气流和外加电场等环境因素同样会影响这些过程，从而影响影响分子荧光的发射。在本项目中我们开展了以下工作：1. 通过脉冲空间整形技术研究了空间整形的激光脉冲与空气、水等物质相互作用产生的荧光、超连续白光发射；2. 通过时间和空间分辨技术研究成丝诱导分子荧光发射过程中发生的分子准直、转动重建、布居捕获和碰撞激发等动力学过程；3.通过改变温度、湿度、气压、气流等因素研究了环境效应对飞秒激光成丝诱导分子荧光的影响；4.利用白光Z扫描技术研究飞秒激光与CS2，ZnSe等物质相互作用过程中非线性光学效应。通过这些研究我们对超短激光脉冲与原子分子相互作用机制以及分子结构和辐射特性有了较为深入的认识，对飞秒激光成丝诱导分子荧光的发射机制有了深入的了解。在此基础上，我们探索出了一些能有效增强飞秒激光成丝诱导分子荧光发射的途径，为利用成丝诱导分子荧光进行远程探测奠定基础。