Second-Harmonic Generation of Super Powerful Femtosecond Pulses Under Strong Influence of Cubic Nonlinearity

A theoretical model of second-harmonic generation (SHG) under strong influence of cubic nonlinearity was verified in experiment. Effective energy conversion in thin potassium dihydrogen phosphate crystals at peak intensity up to 5 TW/cm
$^2$
(B-integral equaled 6.4) was demonstrated and no crystal damage was observed. Comparative analysis of SHG of radiation at the fundamental wavelengths of 910 and 800 nm showed the major advantages of the first one. The double-pass geometry of SHG in an ultrathin crystal on a substrate is discussed in detail. Additional correction of parabolic spectral phase of the SH radiation allows pulse duration to be shortened from 20 to 9 fs for 910 nm fundamental wavelength and from 20 to 12 fs for 800 nm.