Master oscillator power amplifier system for optical parametric conversion of high-energy pulses from 1 to um

The topic of this work has been to convert the wavelength of a high energy 1 μm Nd:YAG laser to 2 μm. In order to achieve high efficiency without compromising beam quality, a two-stage system was designed and implemented in the laboratory. The first stage was an optical parametric oscillator (OPO) that converted a narrow 1 μm beam with about 8 mJ energy to a 2 μm signal of relatively high quality. An optical parametric amplifier (OPA) pumped with up to 500 mJ formed the second stage and used the OPO signal as input. Both stages of the master oscillator/power amplifier (MOPA) system were based on the nonlinear crystal KTiOPO4 (KTP). With 500 mJ pump energy, different OPA configurations produced up to 138 mJ signal energy with M2 ≈ 2.3. Numerical simulations of the MOPA configuration gave good agreement with the experimental results.