Heading To 1 Kw Levels With Laser Bars Of High Efficiency And Emission Wavelength Around 880 Nm And 940 Nm

High-power quasi-CW laser bars are of great interest as pump sources of solid-state lasers generating high-energy ultra-short pulses for high energy projects. These applications require a continuous improvement of the laser diodes for reliable optical output powers and simultaneously high electrical-to-optical power efficiencies. An overview is presented of recent progress at JENOPTIK in the development of commercial quasi-CW laser bars emitting around 880 nm and 940 nm optimized for peak performance.At first, performances of 1.5 mm long laser bars with 75% fill-factor are presented. Both, 880 nm and 940 nm laser bars deliver reliable power of 500 W with wall-plug-efficiencies (WPE) > 55% within narrow beam divergence angles of 11 degrees and 45 degrees in slow-axis and fast-axis directions, respectively. The reliability tests at 500 W powers under application quasi-CW conditions are ongoing. Moreover, laser bars emitting at 880 nm tested under 100 mu s current pulse duration deliver 1 kW output power at 0.9 kA with only a small degradation of the slope efficiency. The applications of 940 nm laser bars require longer optical pulses and higher repetition rates (1-2 ms, similar to 10 Hz). In order to achieve output powers at the level of 1 kW under such long pulse duration, heating of the laser active region has to be minimized. Power-voltage-current characteristics of 4 mm long cavity bars with 50% fill-factor based on an optimized laser structure for strong carrier confinement and low resistivity were measured. We report an output power of 0.8 kW at 0.8 A with > 60% conversion efficiency (52% WPE). By increasing the fill-factor of the bars a further improvement of the WPE at high currents is expected.