Study of ultrafast relaxation dynamics of localized center in solids by femtosecond Raman spectroscopy

1)飞秒激光系统的安装：我们安装了一个高功率飞秒激光系统，该系统提供波长为600和300 nm的泵浦脉冲，在400至950 nm光谱范围内具有白色连续谱的探测脉冲，脉冲持续时间为100 fs。2）碱金属卤化物中的飞秒非线性光谱：a）我们发现KBr中F中心的绝热势能面（APES）上的弛豫过程是动态的，发生在100 fs以内。B）在KBr中F心的形成过程中，F心的形成先于空穴的自陷，F心的弛豫发生在中心型自陷激子（STE）上。c）我们首次观察到了KI中最低APES上STE作为两个极小值之间的波斑的振荡。d）在碱金属碘化物（KI和RbT）中，自由空穴首先转变为单中心自陷空穴，然后形成双中心自陷空穴（V_k中心）。此外，激子自陷的初始阶段不是由类V_k中心和自由电子组成，而是由与电子相关的单中心自陷空穴组成，这是形成STE的先驱态之一。3）ZnTe：O的飞秒非线性光谱：我们观察到了束缚激子的弛豫过程以及与声子的中间耦合。激子-晶格弛豫与LO声子的发射有关，并与LO声子的周期有关。

1)Installation of a femtosecond laser system.We installed a high power femtosecond laser system which provided pumping pulses with wavelengths of 600 and 300 nm,probe pulses with a white continuum in the spectral range of 400 to 950 nm and a pulse duration of 100 fs.2) Femtosecond nonlinear spectroscopy in alkali halides:a) We found that the relaxation process on the adiabatic potential energy surface (APES) of F center in KBr is dynamical and occurs within 100 fs. b) In the formation processes of F center in KBr, an F center is formed before the self-trapping of a hole and the F center relaxation occurs from the on-center type self-trapped exciton (STE). c) We observed for the first time the oscillation of the STE as a wavepaquet between two minima on the lowest APES in KI. d) In alkali iodides (KI and RbT) a free hole is first converted to a one-center self-trapped hole and subsequently a two-center self-trapped hole (V_k center) is formed. Furthermore, the initial stage of self-trapping of a exciton does not consist of a V_k-like center and a free electron but a one-center self-trapped hole correlated with an electron is one of the precursor states for the STE formation. These are the first experimental finding of the initial processes of the self-trapping.3) Femtosecond nonlinear spectroscopy in ZnTe:O: We observed the relaxation processes of bound excitons with the intermediate coupling with phonons. The exciton-lattice relaxation with emission of LO phononsoccurs with a period of the LO phonon.