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

1)安装飞秒激光系统。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，光谱范围为400至950 nm的白色连续体探测脉冲，脉冲持续时间为100 fs。2)碱卤化物的飞秒非线性光谱：a)我们发现KBr中F中心绝热势能面（APES）的弛豫过程是动态的，发生在100 fs内。b)在KBr中F中心的形成过程中，F中心是在空穴自俘获之前形成的，F中心的弛豫来自于on-center型自俘获激子（STE）。c)我们首次观测到在KI最低的ape上，STE以两个极小值之间的波串的形式振荡。d)在碱碘化物（KI和RbT）中，自由空穴首先转化为单中心自困空穴，随后形成双中心自困空穴（V_k中心）。此外，激子自俘获的初始阶段不是由一个类v_k中心和一个自由电子组成，而是一个与电子相关的单中心自俘获空穴是STE形成的前驱态之一。这是自俘获初始过程的第一个实验发现。3) ZnTe:O的飞秒非线性光谱：我们观察了束缚激子与声子的中间耦合弛豫过程。LO声子的激子-晶格弛豫伴随着LO声子的发射而发生。

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.