Abstract

Operating rare earth-doped solid-state lasers at cryogenic temperatures has been proven recently as a means of power scaling with good beam quality while eliminating significant overall design complexity. As compared to room temperature, solids at cryogenic temperatures have much higher thermal conductivity (which significantly facilitates deposited heat removal), smaller thermal expansion coefficients, and often smaller dn/dT (which significantly mitigates thermally-induced gain medium distortions) [1], Rare earth ion f↔f-transition linewidths get narrower, thus increasing the corresponding peak cross sections. It was found that Er³⁺:YAG emission cross section increases three-fold at 1618 mn (⁴I_13/2⟹⁴I_15/2, Y₂→Z₅)and ~2.8-fold at 1645 nm (⁴I_13/2⟹⁴I_15/2, Y₂→Z₇). Besides, in quasi-four-level systems, like Er³⁺, ground state absorption at laser transitions is greatly reduced. So far, known efforts in cryo-cooled diode-pumped lasers have concentrated on Yb-doped materials, and major power scaling results were achieved for Yb³⁺: YAG (e. g., [1]). The only publication on cryo-cooled Er-doped laser goes back to the first flash-lamp pumped laser experiments with Er: YAG [2], but it does not give a clue to the resonantly diode-pumped Er: YAG laser power scaling potential. Etere we report laser performance results for the resonantly diode-pumped Er: YAG cryo-laser, which is indicative of very high laser scaling potential at cryogenic temperatures.

© 2007 IEEE