Title: Single-mode, High Repetition Rate Ho:YLF Laser for Space-borne Lidar Applications
Presenting Author: Jirong Yu
Organization: NASA LaRC
Co-Author(s): Yingxin Bai and Teh-Hwa Wong, Science Systems & Applications, Inc; Mulugeta Petros and Upendra Singh, NASA LaRC

Abstract:
Integrated Path Differential Absorption (IPDA) lidar is an approach for global observation of atmospheric carbon dioxide to achieve the unprecedented accuracy. There are excellent absorption lines for the measurements of CO2 in 2μm wavelength region with regard to the strength of the absorption lines, low susceptibility to atmospheric temperature variability, and freedom from problematic interference with other absorption lines. It is critical to scale the 2.05 μm laser transmitter to higher output power levels in a robust prototype with long-lifetime design features for IPDA lidar instrument. Supported by NASA's Earth Science Technology Office (ESTO) Advanced Components Technology (ACT) program, we are developing a single transverse/longitudinal mode, compact Q-switched Ho:YLF laser. Ho:YLF laser is capable of generating giant pulses because of its long upper level life time and large emission cross-section. Its wavelength can be easily tuned over the absorption line of CO2, R30=2050.967 nm. For the direct detection IPDA lidar, the desired 2 µm Ho:YLF laser should generate 34-40 mJ pulses at the repetition rate of 100 to 200 Hz, with short pulse length (<100 ns) and limited power supply (<800 W). In-band pumped Ho:YLF laser has high efficiency and the ability to operate in high repetition rate (>1 kHz) This Ho:YLF laser is inband pumped by a 40 W Tm:fiber laser. 40 mJ output pulse energies from oscillator at 100 Hz operation and 34 mJ for 200 Hz operation is achieved, respectively. The higher efficiency of 200 Hz operation than that of 100 Hz one is owing the upper level lifetime of Ho:YLF crystal (~14 ms). The peak power exceeds 1 MW corresponding to 32 ns pulse. The near diffraction-limited beam and transform-limited pulse have been measured. The energy requirement of space-borne IPDA lidar has been met without adding amplifier. An engineering packaged laser development is in progress.