On the efficiency of Tm-doped 2µm lasers

K. van Dalfsen; S. Aravazhi; C. Grivas; S. M. García-Blanco; M. Pollnau

doi:10.1117/12.2077490

20 February 2015 On the efficiency of Tm-doped 2μm lasers

K. van Dalfsen, S. Aravazhi, C. Grivas, S. M. García-Blanco, M. Pollnau

Author Affiliations +

Proceedings Volume 9342, Solid State Lasers XXIV: Technology and Devices; 93421U (2015) https://doi.org/10.1117/12.2077490
Event: SPIE LASE, 2015, San Francisco, California, United States

Abstract

A potassium double tungstate layer with the composition KY_0.40Gd_0.29Lu_0.23Tm_0.08(WO₄)₂ was grown onto a pure KY(WO₄)₂ substrate by liquid-phase epitaxy, microstructured by standard lithography and Ar-ion etching, and overgrown by a pure KY(WO₄)₂ layer. The end-facets were polished. Laser experiments were performed on these buried, ridge-type channel waveguides in a resonator with one butt-coupled mirror and Fresnel reflection from the other end-facet, resulting in a high output-coupling degree of 89%, compared to intrinsic round-trip losses of only 2%. By pumping with a Ti:Sapphire laser at 794 nm, 1.6 W of output power at 1.84 μm with a maximum slope efficiency of ~80% was obtained. To the best of our knowledge, this result represents the most efficient 2-μm channel waveguide laser to date. We determined the optimum Tm³⁺ concentration in double tungstate channel waveguides to be at least 8at.% for efficient lasing. The theoretical limit of the slope efficiency depends on the Stokes efficiency which here is 43.2%, the outcoupling efficiency which here is 99%, and the pump quantum efficiency. The pump quantum efficiency of a 2-μm Tm³⁺ laser pumped around 800 nm hinges on the efficiency of its cross-relaxation process. By fitting the macroscopic cross-relaxation parameter which linearly depends on the Tm³⁺ concentration to concentration-dependent luminescence- decay data, calculating the overall decay rate of the pump level, and deriving the concentration-dependent pump quantum efficiency, we obtain a theoretical limit for the slope efficiency of 83% for the chosen Tm³⁺ concentration. The experimental slope efficiency of ~80% closely approaches this limit.

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K. van Dalfsen, S. Aravazhi, C. Grivas, S. M. García-Blanco, and M. Pollnau "On the efficiency of Tm-doped 2μm lasers", Proc. SPIE 9342, Solid State Lasers XXIV: Technology and Devices, 93421U (20 February 2015); https://doi.org/10.1117/12.2077490

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