Optical and optomechanical design of the MERLIN laser optical bench

For the satellite-based methane lidar instrument MERLIN a reliable laser source is needed that emits laser pulses at two wavelengths of around 1645 nm to measure the methane concentration of earth’s atmosphere with an Integrated Path Differential Absorption LIDAR (IPDA). To generate those pulses, the laser (LASO) consists of a seeded, actively qswitched, diode pumped Nd:YAG master oscillator power amplifier (MOPA) and a subsequent seeded and frequencycontrolled optical parametric oscillator (OPO). Due to the passive thermal control of the instrument the laser has to withstand a large non-operational and operational temperature range and also high mechanical loads while at the same time a compact envelope is required. Together with the demanding requirements on the laser performance a very robust optical design is needed. To meet those requirements, Fraunhofer Institute for Laser Technology (ILT) uses optomechanical mounts that were developed in a previous project and show very low tilting over a large operational temperature range, even after nonoperational temperature cycling and applying mechanical loads. The mounts are soldered and free of organic substances as the LASO is enclosed in a pressurized housing (LASH). Any outgassing could lead to a decay or damage of the optics and thus a failure of the laser. During the development of the optomechanical mounts many tests were performed to quantify the statistical behavior under mechanical and thermal loads. Based on those results and additional mechanical simulations, Monte-Carlo-Analyses have been performed to analyze the performance of the laser and to verify the fulfilment of the requirements.