利用飞秒激光泵浦探测技术，通过改变光学参数，如中心波长、功率，分别对未故意掺杂高纯n型砷化镓的差分反射谱进行研究，进而分析室温下砷化镓光生载流子动力学过程.首先，当泵浦光功率恒为100 mW，探测光功率恒为10 mW时，随着中心波长的增大，差分反射率峰值随之增大，信噪比也随之增加.其次，通过拟合不同延迟时间下泵浦光功率和差分反射率的实验曲线，并和理论模型比较后发现，在一定范围内的泵浦功率和差分反射率呈线性相关，未故意掺杂高纯n型砷化镓的饱和载流子浓度为(3.590 1±0.310 3)×1017 cm－3.在此基础上,把光生载流子动力学过程分为3个过程：804±67 fs的光激发过程、134 ~268 fs的初始散射过程、1 ps和3～6 ps的复合过程.研究表明，差分反射率与探测功率不存在显著的依赖性，但差分反射谱的信噪比与探测功率存在相关性.

Varied with some optical parameters, such as center wavelength, power, the differential reflectance spectroscopy of unintentionally doped high-purity n-type gallium arsenide were studied by femtosecond laser pump probe technique. These time-resolved differential reflective spectroscopy further analyzed the dynamics of photo-induced carrier of gallium arsenide at room temperature. Firstly, if the pump and the probe power were stabled at 100 mW and 10 mW respectively, the peak differential reflectivity increases with the red shift of center wavelength, and the signal-to-noise ratio increases as well. Secondly, Based on the fitting experimental data of varying pump power and the theoretical model, it is found that there is a linear correlation between the pump power and the differential reflectance in a certain range, through which the saturated carrier concentration of this gallium arsenide sample was calculated as (3.590 1±0.310 3)×1017 cm－3. Thirdly, the dynamics process of photo-induced carriers is divided into three terms: the photo-excitation process (804±67 fs), the initial scattering process (134 ~268 fs), the recombination process with 1 picosecond and 3~6 ps. Last but not least, it seems that the differential reflectance has no significant dependence on the probe power, but the signal-to-noise ratio of the differential reflectance spectrum is correlated with the probe power. In a word, this work not only investigates the ultrafast dynamics of unintentionally doped high purity n-type gallium arsenide, which provides a reference for other materials, but also offers the optimal experimental parameters of pump-probe spectroscopy.