High power Er:YAG laser at 1646nm pumped by an Er/Yb fibre laser

Abstract

Solid-state lasers operating in the eye-safe wavelength regime around ~1.5-2.1 µm regime have numerous applications. For many applications, the requirement for high power is accompanied by the need for high efficiency and good beam quality, which are difficult to achieve in conventional solid- state lasers because of thermal effects. Fibre lasers are less affected by thermal effects, but pulse energies are limited by amplified spontaneous emission and by damage to the fibre end facets. An alternative approach which circumvents this problem is to use a hybrid laser where a fibre laser is used to 'in-band' pump a bulk solid-state laser. In this paper we describe an Er:YAG laser pumped by a tunable, cladding-pumped Er/Yb fibre laser and discuss factors affecting the laser performance. Five crystals with Er-concentrations in the range 0.25% to 4 at% and with crystal lengths selected for ~95% absorption of the pump light at 1532nm were used, and the laser performance was investigated for a range of output coupler transmissions (2-30%) at 1646nm. In preliminary experiments we have achieved a maximum output power of 4W at 1646nm for 11W of absorbed pump power corresponding to an efficiency of 36%, using a crystal with 0.5 at% Er-concentration and an output coupler transmission of 10%. Our experiments have revealed that the cw efficiency decreases quite markedly for higher Er-concentrations. The origin this behaviour is the subject of further investigation and our findings will be presented. The prospects for further increase in output power and efficiency will also be discussed.

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ORCID for J.K. Sahu: orcid.org/0000-0003-3560-6152

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