6.5 kW, Yb:YAG Ceramic Thin Disk Laser
Technical note 1 Jan-1 Dec 2010
AIR FORCE RESEARCH LAB KIRTLAND AFB NM DIRECTED ENERGY DIRECTORATE
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The operation of a 1030 nm, single, thin disk laser which produced 6.5 kW of laser output power with 57 percent slope efficiency is reported. The YbYAG ceramic gain element is 200 micrometer thick, bonded to a 1 mm, undoped, ceramic YAG cap. The gain element is pumped by diodes at 940 nm. The maximum incident pump intensity was 5 kWcm2, which yielded an output intensity of 2.6 kWcm2 of multimode laser radiation. Rigrod analysis suggests that the laser operates with inhomogeneous gain saturation. This is attributed to the enhanced, spatial-hole-burning effect when the gain element is adjacent to a mirror. The pump threshold and output intensities were independent of pump spot size, which validates area scaling. Observed thermal lensing contributions include thermal-expansion-induced disk flexure, pump-edge-induced temperature profile and a strong thermal imprint of the cooling nozzle due to the direct jet impingement on the high reflection HR coated side. Weak absorption of the 1030 nm intracavity intensity in the undoped cap andor the anti-reflection AR coating led to excess heating that limited the extracted power intensity. These results suggest ceramic YbYAG can be scaled to higher powers using optimized thin disk elements and improved disk thermal management techniques.
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