Efficient continuous wave deep ultraviolet Pr³⁺: LiYF₄ laser at 261.3 nm

We report continuous wave deep ultraviolet laser operation at 261.3 nm by intracavity frequency doubling of laser diode pumped Pr³ doped LiYF₄ lasers. Using two InGaN laser diodes with a maximum output power of about 1 W each, a 2.9 mm long Pr³:LiYF₄ crystal and a 5 mm long beta-barium-borate crystal, coherent radiation with an output power of 481 mW at 261.3 nm was achieved at an optical-to-optical efficiency of 26.1 with respect to the total pump power. Both, linear and nonlinear losses have been calculated to be approximately 0.6 by using a model for intracavity frequency doubling with focussed Gaussian beams.