Efficient Mid-Infrared Femtosecond Optical Parametric Amplifier Based on LiGaS 2

We demonstrate an efficient femtosecond mid infrared (MIR) femtosecond optical parametric amplifier (OPA) based on the LiGaS2(LGS) crystal. We show that transferring the gain to the pre-amplifier stage is a convenient and efficient approach to improve the conversion efficiency and avoid the crystal damage caused by excessive pump intensity. Through this approach, femtosecond pulses tunable over 4–10 μm, with up to 23.3% quantum conversion efficiency is obtained. An average power of 150 mW is obtained at 8 μm. Considering the losses of the optical elements, the quantum conversion efficiency is corrected to be 30.3% at 8 μm. As far as we know, this represents the highest conversion efficiency of femtosecond OPAs based on a Type-I-phase-matched LGS crystals. The system shows excellent power stability, with a root-mean-squared variation of 0.46% over 6 hours.