On the efficiency of Tm-doped 2μm lasers

Abstract

A potassium double tungstate layer with the composition KY 0.40 Gd 0.29 Lu 0.23 Tm 0.08 (WO 4 ) 2 was grown onto a pure KY(WO 4 ) 2 substrate by liquid-phase epitaxy, microstructured by standard lithography and Ar-ion etching, and overgrown by a pure KY(WO 4 ) 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 endfacet, 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 Tm 3+ 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 Tm 3+ 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 Tm 3+ concentration to concentration-dependent luminescencedecay 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 Tm 3+ concentration. The experimental slope efficiency of ~80% closely approaches this limit.

CONTINUOUS-WAVE MICROCHIP LASER GENERATION OF Tm:KLu(WO4)2 AND Tm:KY(WO4)2 CRYSTALS

“…122-128 Dernovich O.P. et al Приборы и методы измерений 2016 Введение В последнее время динамично развиваются и исследуются лазеры, в которых в качестве ак-тивного элемента используются кристалличе-ские материалы, легированные трехвалентными ионами тулия [1][2][3]. Такие материалы испускают излучение на длинах волн около 2 мкм, которое востребовано для практических применений в прецизионной обработке материалов [4], биоме-дицине [5], дальнометрии [6] и др.…”