Double-pass Tm:Ho:YLF amplifier at 2.05 μm for spaceborne eye-safe coherent Doppler wind lidar and CO2 differential absorption lidar (DIAL)

Accurate global atmospheric remote sensing such as wind and carbon-oxide concentration profiling requires a coherent Doppler lidar and a Differential Absorption Lidar (DIAL) in an eye-safe spectrum range, respectively. Both Doppler lidar and DIAL should have laser transmitters with high pulse energy and high efficiency. There is no doubt that a Tm:Ho:YLF or Tm:Ho:LuLF laser oscillator with multistage amplifiers are appropriate candidates for these transmitters, especially for space-borne lidar systems. To achieve a high efficient laser transmitter, a collinear double-pass Tm:Ho:YLF laser amplifier has been designed and experimentally tested with a Tm:Ho:YLF laser oscillator. When laser pulses at a reasonably high energy, said 50 mJ here, from a Q-switched Tm:Ho:YLF laser oscillator were directly sent into a single-pass Tm:Ho:YLF amplifier, a gain of 1.86 was obtained at a pump pulse energy of 5.82 J. With a collinear double-pass configuration, a gain of 2.24 was achieved at same pump pulse energy level including all losses of the necessary optical elements, such as a thin film polarizer, a half-wave plate, and a Faraday rotator. More than 95% pulse energy was extracted from the double-pass amplifier, compared to a single-pass amplifier.