Highly efficient second-harmonic generation of intense femtosecond pulses with a significant effect of cubic nonlinearity

A highly efficient (73 %) second-harmonic generation of femtosecond pulses in a 1-mm-thick KDP crystal at a fundamentalharmonic peak intensity of 2 TW cm^-2 has been demonstrated experimentally. In a 0.5-mm-thick KDP crystal, a 50 % efficiency has been reached at a peak intensity of 3.5 TW cm^-2. We examine the key factors that limit the conversion efficiency and present numerical simulation results on further temporal compression of second-harmonic pulses.