Influence of the group-velocity mismatch in frequency conversion of picosecond pulses

The efficiency of second-harmonic generation and the degree of compression of picosecond pulses from a neodymium glass laser were enhanced by a delay between ordinary and extraordinary pulses interacting in KDP crystals. The conversion efficiency was increased by a factor of 1.5 (from 33 to 50%) and the second-harmonic pulses were compressed by a factor of 2.4 (from 4.8 to 2 ps).