Feasibility and performance study for a space-borne 1645 nm OPO for French-German satellite mission MERLIN

We present a theoretical and experimental analysis of a pulsed 1645 nm optical parametric oscillator (OPO) to prove the feasibility of such a device for a spaceborne laser transmitter in an integrated path differential absorption (IPDA) lidar system. The investigation is part of the French-German satellite mission MERLIN (Methane Remote Sensing Lidar Mission). As an effective greenhouse gas, methane plays an important role for the global climate. The architecture of the OPO is based on a conceptual design developed by DLR, consisting of two KTA crystals in a four-mirror-cavity. Using numerical simulations, we studied the performance of such a setup with KTP and investigated means to optimize the optical design by increasing the efficiency of the OPO and decreasing the fluence on the optical components. For the experimental testing of the OPO, we used the INNOSlab-based ESA pre-development model ATLAS as pump laser at 1064 nm. The OPO obtained 9.2 mJ pulse energy at 1645 nm from 31.5 mJ of the pump and a pump pulse duration of 42 ns. This corresponds to an optical/optical efficiency of 29%. After the pump pulse was reduced to 24 ns, a similar OPO performance could be obtained by adapting the pump beam radius. In recent experiments with optimized optical design the OPO obtained 12.5 mJ pulse energy at 1645 nm from 32.0 mJ of the pump, corresponding to an optical/optical efficiency of 39%. Two different methods were applied to study the laser damage thresholds of the optical elements used.