Second harmonic generation in plasmas produced by intense femtosecond laser pulses

Plasmas were produced by tightly focusing femtosecond laser pulses onto the surface of metal films and glass targets. A relatively intense, well-collimated second harmonic could be observed in the specular direction. The conversion efficiency reached 10/sup -4/ for focused intensities around 10/sup 16/ W/cm/sup 2/. Detailed measurements of the angular dependence, the polarization properties, and the second-harmonic frequency spectra were performed. Time-resolved pump-probe experiments revealed interesting information about the dynamics of the plasmas. It is suggested that resonant absorption plays an important role in second-harmonic generation.<
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