High-Beam-Quality, High-Average-Power Yb:YAG Lasers

Precision tracking of airborne targets, atmospheric sensing, and active imaging require high-average-power, high-beam-quality laser sources. We propose to address these requirements through the use of a diode-side-pumped, multi-pass-slab (MPS), Yb-doped laser where high beam quality is achieved by multi-passing the fundamental mode of the laser resonator several times through the gain region to efficiently extract the stored energy. The pump sources will be coupled to the Yb-doped crystal using multimode fibers, allowing for flexibility in design and for the laser output power to be scaled to hundreds of Watts by increasing the number of fibers pumping the crystal or the pump power in each fiber. In our design, heat is removed from the laser crystal by direct contact to heat sinks; flowing liquid contacting the crystal is not required as it is in other schemes, allowing the use of a wide variety of cooling methods. Cooling to as low as liquid-nitrogen temperatures will be explored to improve the laser efficiency, thermo-optic properties, and reduce the possibility of optical damage when Q-switched. Thermal lensing, which can cause aberration of the output beam, is kept low by spreading the heat load over a large area and minimizing the distance between the heat load and heat sinks.