Abstract
We report on Tm:YLF and Tm:LLF slab lasers (1.5 x 11 x 20 mm3) end pumped from one end with a high-brightness 792 nm laser diode stack. These two lasers are compared under identical pump conditions in continuous-wave regime. A stronger negative thermal lens in Tm:LLF than in Tm:YLF is highlighted, making it more difficult to operate the Tm:LLF laser under stable lasing conditions. In a configuration where the high reflectivity cavity mirror has a radius of curvature of r = 150 mm, the Tm:YLF (Tm:LLF) laser produces a maximum output power of 150 W (143 W) for 428 W of incident pump power (respectively). For a second cavity configuration where the high reflectivity cavity mirror has a radius of curvature of r = 500 mm, the Tm:YLF laser produces a maximum output power of 164 W for 412 W of incident pump power and a 57% slope efficiency with respect to the absorbed pump power. The emitted wavelength of these two lasers are measured as a function of the output coupler reflectivity and it shows that Tm:LLF laser emits at a longer wavelength than Tm:YLF.
Highlights
High-power and high-energy lasers at 2 μm can be used for processing of materials that are transparent at 1 μm and are difficult to process with established industrial laser systems
We report on Tm:YLF and Tm:LLF slab lasers (1.5 x 11 x 20 mm3) end pumped from one end with a high-brightness 792 nm laser diode stack
Acknowledgments Supporting data are available from the Heriot-Watt Research Portal https://researchportal.hw.ac.uk and may be used under a Creative Commons Attribution License
Summary
High-power and high-energy lasers at 2 μm can be used for processing of materials that are transparent at 1 μm and are difficult to process with established industrial laser systems. In 2006, an output power of 70 W from a Tm:YLF slab laser end-pumped with a 300 W diode stack was reported by So et al [2], the slope efficiency was 44% with respect to the absorbed pump power. In 2009, Schellhorn et al demonstrated a dual-end-pumped Tm3+:YLF slab laser producing 148 W output at 1912 nm with a slope efficiency of 41% with respect to absorbed pump power [3]. In 2013, using an Innoslab pump architecture, a Tm:YLF laser with 200 W of output at 1908 nm and a slope efficiency of 52% with respect to the absorbed pump power, was reported by Li et al [6]. We analyze the wavelength behavior of these two crystals as a function of output coupler reflectivity, at maximum output power, to find the best match for pumping holmium doped materials
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