电子自旋偏振度及其弛豫过程的飞秒激光吸收光谱研究

基于二能级体系的速率方程，获得了非完全初始自旋偏振极化条件下的自旋偏振向上和向下 载流子布居弛豫的解析解. 基于小信号近似，给出了左、右旋圆偏振探测光的饱和吸收变化 的表达式. 此表达式中含有电子布居的初始自旋偏振度参数，因而用此表达式拟合实验数据 能够直接获取电子布居的初始自旋偏振度，而电子布居的初始自旋偏振度在自旋偏振输运研 究中是一个非常重要的关键参数. 实验获得了GaAs/AlGaAs多量子阱结构中光注入电子布居 的初始自旋偏振度及其弛豫时间常数. 关键词： 圆偏振抽运_探测技术 电子自旋偏振度 自旋偏振弛豫 GaAs量子阱

Electron-spin polarization and its relaxation probed by femtosecond laser absorption

Based on the rate equations of a two_level system, the analytical solutions of r elaxation of carrier populations with spin_up and spin_down polarization are obt ained under the condition of incomplete initial spin polarization. In the small signal regime, the saturated absorption_change expression of right_ and left_cir cularly polarized probe beam is given. The parameter, initial degree of spin pol arization of electron population, appears in the expression. Therefore, the init ial degree of spin polarization of electron population, which is a very importan t key parameter in the transport of spin polarization, can be extracted by fitti ng the expression to the saturated absorption trace obtained experimentally. Fin ally, the initial degree of spin polarization of photo_injected electron populat ion and its relaxation time constant in GaAs/AlGaAs multiple quantum wells are a cquired in experiments.