Thermal Lens Manipulation Using Edge-Heaters in Laser Bars for Improved Efficiency and Divergence

We present here an approach to flattening the lateral thermal lens that develops in kW-class semiconductor laser bars consisting of multiple broad-area emitters and is responsible for limiting the power, conversion efficiency and beam quality of the bars. Simulation results show that by increasing heat at the edge-emitters of the bars, thermal lens can be diminished. With an experiment on single-emitters, we demonstrated that the required heat in the edge-emitters can be achieved by shortening their pump length. Following these studies, we fabricated 1-cm wide bars containing 37 emitters, each with a 186-μm-wide stripe and a 4-mm-long resonator. In contrast to the baseline bars with equally and fully pumped emitters, the best-designed bars with an optimum (shorter) pump length only in the edge-emitters yield a 5%-points higher conversion efficiency, and an improved beam quality, narrowing the lateral beam divergence at 95% power content by over 10% at 0.8 kW power.