超快光克尔门选通时间分辨拉曼光谱技术研究

Femtosecond time-resolved Raman spectroscopy technique is an important tool to investigate the structure changes dynamics of transient species and electronic excited states of materials. In traditional time-resolved Raman measurements, however, the background fluorescence interference originated from the compound of interest itself often makes the Raman scattering signals unusable. In this project, we propose a time-resolved Raman spectroscopy based on ultrafast optical Kerr gating technique, which makes use of the time difference between the background fluorescence and Raman scattering light. By rejecting the long-lived fluorescence using the ultrafast optical gate, time-resolved Raman scattering measurements with high signal-to-noise ratio (SNR) and ultrafast time-resolution can be realized. The study includes: (1) Investigating the influence of self-diffraction effect on optical Kerr measurements and improving the SNR and time-resolution of the ultrafast optical Kerr gated (OKG) time-resolved Raman measurements. (2) Improving the universality of the time-resolved OKG Raman spectroscopy technique for excited molecules, by developing the wavelength-tunable pump light source based on supercontinuum generation induced by femtosecond laser pulses. The final goal of the project is to set up the time-resolved micro-Raman spectroscopy system based on ultrafast optical Kerr gating technique, and explore its application in research on the dynamics of some photochemistry and photobiology reactions. The system is characterized by a time-resolution less than 1 ps and spatial resolution better than 10 μm.

飞秒时间分辨拉曼光谱技术是研究光生瞬态物种结构变化以及材料电子激发态结构的重要手段之一。在传统时间分辨拉曼光谱检测中，样品分子自身荧光的干扰限制了激发态拉曼光谱检测技术的应用。为此，本项目提出一种基于超快光克尔门的时间分辨拉曼光谱测量技术，该技术利用拉曼光与荧光时间特性的差异，利用时间门选通拉曼光、抑制荧光干扰，可实现具有高信噪比和高时间分辨率的拉曼光谱测量。本项目的主要研究内容包括：研究超快光克尔门中自衍射效应的抑制技术，实现具有高对比度的超快光克尔门，以提高时间门选通拉曼光谱检测的信噪比和时间分辨率；研制基于飞秒激光诱导产生超连续白光的波长可调谐泵浦光源，以提高激发态分子拉曼光谱检测的通用性；搭建基于超快光克尔门选通技术的时间分辨微区拉曼光谱检测系统，系统时间分辨率优于1 ps，空间分辨率优于10 μm；探索该技术在飞秒激光诱导材料光化学、光生物反应等超快动力学过程研究中的应用。

时间分辨拉曼光谱技术是研究光生瞬态物种结构变化以及材料电子激发态结构的重要手段之一。在传统时间分辨拉曼光谱检测中，样品分子自身荧光的干扰限制了激发态拉曼光谱检测技术的应用。本项目提出一种基于超快光克尔门的时间门选通拉曼光谱测量技术，该技术基于拉曼光与荧光时间特性的差异，利用时间门选通拉曼光、抑制荧光干扰，可实现具有高信噪比和高时间分辨率的拉曼光谱测量。项目取得的创新性研究成果如下：. 1、研究了均匀稳定飞秒超连续白光的产生与啁啾调控技术，提出了一种基于微透镜阵列的高强度、稳定超连续白光产生的新方法，利用微透镜阵列结合4f成像系统在透明介质中并行产生多重细丝通道，输出超连续白光功率密度提高了两个数量级；. 2、研究了飞秒时域泵浦-探测中自衍射等相干效应的产生机制，通过对光克尔信号的成像直接观测到了光克尔信号中的自衍射效应，通过调控泵浦光和探测光偏振态，有效抑制了自衍射效应的影响，实现了具有高信噪比的超快光克尔门；. 3、利用时间门选通的方法从含有荧光材料的纯净水中成功提取出水分子的拉曼信号，实现了荧光背景噪声的有效抑制；建立了一种基于飞秒激光脉冲的单光束相干反斯托克斯拉曼散射（CARS）光谱测量系统，利用单光束飞秒激光可实现微区内的拉曼光谱测量；. 4、利用时间分辨荧光、时间分辨瞬态吸收谱等超快光谱测量技术，研究了石墨烯复合材料、荧光量子点及二维硫化物等纳米材料光致发光等过程中光生载流子超快动力学。.