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采用Z-扫描和泵浦-探测技术，在光通讯波段对砷化镓( GaAs)单晶进行了非线性动力学以及非线性光学的实验研究。飞秒泵浦-探测实验结果表明，三阶非线性光学效应源于砷化镓单晶对飞秒激光的瞬态双光子吸收，而五阶非线性光学效应源于砷化镓单晶双光子吸收诱导的自由载流子吸收效应。通过Z扫描实验，得到了关于GaAs单晶所有的非线性光学参数，包括双光子吸收系数、三阶非线性折射系数、双光子吸收诱导的自由载流子吸收截面以及双光子吸收诱导的自由载流子折射截面。结果表明，砷化镓单晶在制造光限幅器件和光电探测器方面具有良好的发展前景。“,”We report experimental investigations of nonlinear dynamics and optical nonlinearities of GaAs single crystal in the telecommunication windows. Femtosecond time-resolved degenerate pump-probe measurements indicate that the observed third-order nonlinear process originates from the instantaneous effect whereas the fifth-order effect arises from two-photon absorption (2PA) induced free-carrier nonlinearities. By performing the Z-scan experiments with femtosecond laser pulses at the wavelengths of 1 300 nm and 1 500 nm, we determine all nonlinear parameters of GaAs crystal, including 2PA coefficient, third-order nonlinear refraction index, 2PA-induced free-carrier absorption cross section, and 2PA-induced free-carrier refraction cross section. These results suggest that GaAs crystal is a promising candidate for applications on optical limiting and photodetector at the telecommunication wavelengths.