A high-brightness QCW pump source using a pre-aligned GRIN lens array with refractive beam correction
We demonstrate a technique for collimating conduction-cooled QCW diode laser stacks that achieves very high brightness in a compact and robust package. First we collimate the bars in the fast-axis using a pre-aligned array of Doric™ GRIN cylindrical lenses, where each lens is oriented to correct the gross positioning errors of each bar. We then measure the residual beam errors using a proprietary wavefront mapping system, and fabricate a refractive wavefront correction phaseplate to effectively flatten the wavefront. The type of lens used exhibits particularly low aberration in the presence of misalignment, ensuring that the resultant wavefront can be effectively corrected. We applied the
technique to two 0.5 mm pitch, 12-bar stacks operating at 1.2 kW. By this method, we repeatably obtained a 10-fold increase in stack brightness, reducing fast-axis beam divergence for the entire stack to below 0.3°, close to the theoretical limit. The result is an extremely compact, high brightness source optimised for side-pumping thin slab lasers.