Second-harmonic generation of amplified femtosecond Ti:sapphire laser pulses

We study theoretically and experimentally second-harmonic generation (SHG) of 150-fs-duration amplified Ti:sapphire laser pulses at a wavelength of 780 nm in the nonlinear crystal KDP of different lengths and at different power densities as high as 150 GW cm(-2). The experimentally observed SHG conversion efficiency does not exceed 50%. It is shown theoretically that one possible process limiting the SHG efficiency at low as well as at high intensities is the modulation of the phase of the fundamental wave. In addition, continuum generation is observed at high intensities and can decrease the SHG efficiency.