The pump-probe technique is an effective method to investigate ultrafast dynamics. And it is widely used in fundamental and application fields of Physics, Chemistry and Biology. The dynamics of bulk GaAs was investigated by femtosecond laser. By changing the area of pump spot, different laser fluences were obtained to excite electron from valence states to conduction states. And it was found that the amplitude of reflectivity change is different. When the carrier density N is 1.44×10^18/cm^3, the change of refraction index is about Dnc=-3.33×10^-5. And when N is0. 36×10^10/cm^3, the change is -2.0×10^-5.
The pump-probe technique is an effective instrument for investigating ultrafast dynamics. It is widely used in fundamental research and application fields, such as Physics, Chemistry and Biology. First introduced is the effect process between femtosecond laser and matter. And set forth is the fundamental of ultrafast phenomena and theory foundation of data disposal. Then introduced is the demand of making samples in experiment, experiment equipment, and the theory of strain pulse. We detect transient reflectivity change on surface of GaAs at different delayed time using femtosecond transient reflection spectroscopy. The changing curve consists of three parts： original scattering process of 100 fs, carriers-lattice thermal equilibrium of l. 5 ps and recombination process of 500 los.
YUAN Dong-qing ZHOU Ming DAI Qi-xun YUAN Run LIU Hui-xia REN Nai-fei CHEN Lei
