Efficient, high power 780 nm pumps for high energy class mid-infrared solid state lasers

Abstract

Mid-infrared (MIR) solid state lasers based on thulium and holmium-doped crystals are of increasing interest in applications in medicine, material processing and particle physics. Thulium-doped lasers can be efficiently pumped at wavelengths around 780 nm and diode laser pumps with high conversion efficiency and high intensity are sought at this wavelength. Diode lasers integrated in laser stacks suitable for high duty cycle pumping are of particular interest for high energy class applications, especially when realizable without need for the additional cost and reliability hazard of microchannel cooling. However, high efficiency and reliable power is more challenging to realize at 780 nm than around 940…980 nm, due to limitations on the capability of the available semiconductor materials. Progress is therefore presented here in the design, realization and test of 780 nm pump sources suitable for high energy class pump applications, using GaAs-based TM-polarized diode lasers. We show how power per device can be increased from 4 W for conventional single emitters (90…100 μm) up to 60 W at high duty cycle (10%) and long pulse length (10 ms) for high brightness large aperture emitters (with 1200 μm aperture, equivalent to around 500 W per bar), at the cost of reduced operating efficiency (from 60 to 50%). We show progress in integrating these large aperture emitters into novel passively (macro-channel) edge-cooled stacks, that are then suitable for use in pumping high energy class Th:YAG laser systems.