A novel method based on a birefringent crystal is presented to compensate for the group-velocity mismatch between a femtosecond pulsed pump and the signal or idler in an optical parametric generator (OPG). With a thin calcite plate inserted between two β-barium borate crystals for synchronization, an efficient four-pass OPG pumped by a frequency-doubled ~200-fs Ti:sapphire laser is obtained. The conversion efficiency is almost doubled throughout 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 significantly by use of this new four-pass OPG to generate the seed.
© 2001 Optical Society of America
(190.4970) Nonlinear optics : Parametric oscillators and amplifiers
(260.1440) Physical optics : Birefringence
(320.5550) Ultrafast optics : Pulses
(320.7160) Ultrafast optics : Ultrafast technology
Yu-Chuan Chen, Xiao-Jun Fang, Jian Li, Xiao-Yan Liang, Heng-Li Zhang, Bao-Hua Feng, Xiu-Lan Zhang, Ling-An Wu, and Zu-Yan Xu, "Efficient Femtosecond Optical Parametric Generator with a Birefringent Delay Compensator," Appl. Opt. 40, 2579-2582 (2001)