Efficient femtosecond optical parametric generator with a birefringent delay compensator

A novel method based on a birefringent crystal is presented to compensate f or the group-velocity mismatch between a femtosecond pulsed pump and the si gnal or idler in an optical parametric generator (OPG). With a thin calcite plate inserted between two p-barium berate crystals for synchronization, a n efficient four-pass OPG pumped by a frequency-doubled similar to 200-fs T i:sapphire laser is obtained. The conversion efficiency is almost doubled t hroughout the whole tunable region compared with a conventional OPG pumped at the same power density, indicating that the total conversion efficiency of femtosecond optical parametric amplifier system can be raised significan tly by use of this new four-pass OPG to generate the seed. (C) 2001 Optical Society of America.