电子自旋偏振度及其弛豫过程的飞秒激光吸收光谱研究

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

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 .

Based on the rate equations of a two-level system, the analytical solutions of relaxation of carrier populations with spin-up and spin-down polarization are obtained under the condition of incomplete initial spin polarization. In the small signal regime, the saturated absorption-change expression of right- and left-circularly polarized probe beam is given. The parameter, initial degree of spin polarization of electron population, appears in the expression. Therefore, the initial degree of spin polarization of electron population, which is a very important key parameter in the transport of spin polarization, can be extracted by fitting the expression to the saturated absorption trace obtained experimentally. Finally, the initial degree of spin polarization of photo-injected electron population and its relaxation time constant in GaAs/AlGaAs multiple quantum wells are acquired in experiments.