Abstract
High-energy 2-μm holmium lasers have a range of important applications including LIDARS for remote sensing and atmospheric science. In addition, such lasers are ideal for pumping nonlinear conversion stages based on ZnGeP2 for generating radiation in the 3-5 µm and 8-12 µm atmospheric transmission windows. Holmium lasers can be pumped at 800 nm by co-doping with Tm or at 1.9 µm by using Tm:fiber lasers [1-5]. The latter approach enables highly efficient end-pumping by optimizing the spatial overlap between the pump and the laser mode. Holmium lasers are quasi three-level systems at room temperature. The population of electrons in the lower laser level can be drastically reduced by cryogenic cooling, and the laser then becomes a quasi four-level system, with potential for higher gain, increased energy extraction efficiency, and reduced bleaching of the pump absorption process, compared to room-temperature operation. We here demonstrate a cryogenically cooled Q-switched Ho:YLF laser, which operates at 1-20 Hz repetition rate and has a pulse energy to pump power efficiency of up to 5.5 J/kW.
© 2013 IEEE
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