Optical parametric master oscillator and power amplifier for efficient conversion of high-energy pulses with high beam quality

We describe a system for parametric conversion of high-energy, Q-switched laser pulses from 1.064 µm to 2.1 µm in KTiOPO4. High beam quality and efficiency are obtained by use of a two-stage system: An optical parametric oscillator (OPO) pumped by a narrow beam with 8 mJ of energy, generates 1.9 mJ of signal energy for seeding an optical parametric amplifier (OPA). With 500 mJ pump energy, different OPA configurations produce up to 138 mJ signal energy with M^2 ≈ 2.3.