Experimental study of frequency shift of reflected microwave from laser-induced plasma

Frequency downshift and upshift of microwaves reflected by laser-induced plasma were experimentally studied. In the experiments, the microwave produced by a microwave generator impinged on the laser-induced plasma. The frequency of the microwave reflected by the pulsed plasmas was measured by a spectrum analyzer. Both in plasma expansion and extinguishing processes, the maximal frequency shift of the reflected microwave was found to be a function of laser power density and the frequency of the incident microwave. The results show that the maximal frequency shift monotonously increases with increasing the laser power density, and decreases with increasing the frequency of the incident microwave．