The effect of oxygen defects on the gradual degradation rates of power and nonradiative carrier recombination in ~800 nm laser diodes was studied experimentally. While intentional introduction of oxygen at low levels (<5×10^15 cm^-3) was observed to degrade lasing performance prior to aging, no variation in gradual degradation rate of lasing power was observed. This suggests that degradation in these devices is not due to nonradiative recombination at low levels of point defects. Simulation of our data indicates that the power degradation may arise from increased intracavity absorption.
Power handling capabilities of broad-area high-power diode lasers are limited by the heat extraction capabilities of the device packaging. Traditional methods of heat extraction rely on conductive heat extraction from the diode chip and an emitting facet in contact with either quiescent or naturally convecting air. This leads to a thermal profile in the lasing direction of the cavity and a hot emitting facet. A hot facet accelerates material degradation, reducing the mean time to failure and limiting the safe operating power. Direct contact between the facet and a liquid coolant could enable higher levels of heat extraction compared to traditional cooling pathways. An innovative approach to cooling high-power, broad-area diode lasers via total immersion in liquid coolant is proposed and tested. In this study, we demonstrate that single emitters can operate with the emitting facet in direct contact with static coolant, with no negative change to device power or efficiency. Thermal analysis and models show that immersed diodes operate with improved thermal pathways, yielding lower total thermal resistance with the greatest improvement to thermal resistance at the facet-fluid interface.
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