High energy diode pumped Ho:Tm:LuLiF_4 laser for Lidar application

摘要

Two-micron lasers can be used in a variety of remote sensing and medical applications. In recent years, such lasers have been used for remote sensing of wind and CO_2 to expand our understanding of the global weather system. The detection of clear air turbulence and wake vortex from aircraft has been proven to enhance air travel safety. In this paper, we present the design and performance of a high-energy diode pumped solid-state 2-micron laser transmitter. There has been a large body of work on 2μm laser crystals using Tm and Ho ions doped in YLF and YAG hosts, but the use of LuLiF_4 as a host is relatively recent. Studies comparing Ho:LuLiF_4 and Ho:YLF show that both crystals have similar emission cross-sections for both 2.05μm and 2.06μm transitions. Tm:Ho:LuLiF_4 has proven to produce 15%-20% more energy than Tm:Ho:YLF. This is primarily attributed to the variation of the thermal population distribution in the Ho: ~5I_7 and ~5I_8 energy levels. The laser crystal used for this experiment is grown in the crystalline a-axis. The resonator is a bow tie ring configuration with 3-m length. One of the mirrors in the resonator has a 3.5m curvature, which sets up a 1.8 mm TEMoo mode radius. The output mirror reflectivity is 72% and it is the dominant source of the resonator loss. An acousto-optic Q-Switch with Brewster angle switches the Q of the oscillator and defines the polarization of the laser output. This laser has a potential to produce a multi joule energy and replace the traditionally used Ho: Tm: YLF crystal.