Mechanisms and fast kinetics of the catastrophic optical damage (COD) in GaAs‐based diode lasers

Abstract

Semiconductor lasers are the most efficient manmade narrow-band light sources and convert up to threequarters of electric energy into light. High-power diode lasers are characterized by very high internal power densities in their small cavity, resulting in local heating and sometimes device degradation. Catastrophic optical damage (COD) of diode lasers is a relevant degradation mechanism and limit for reaching ultrahigh optical powers. An overview is given on research activities targeting the mechanisms being relevant for the COD process in GaAs-based diode lasers emitting in the 630-1100 nm range. The discussion of experiments, where COD is artificially provoked, represents the main topic. The sequence of events and fast kinetics taking place on a nanosecond to microsecond time scale are addressed. A particular emphasis is laid on recent experimental work performed in the authors' laboratories. Paving the way for knowledge-based solutions towards more robust diode lasers represents the ultimate goal of this work. COD diagram determined for a batch of broad-area AlGaAs diode lasers. The time to COD within a single current pulse is plotted versus the actual average optical power in the moment when the COD takes place. Full circles stand for clearly identified COD events (right ordinate), whereas open circles (left ordinate) represent the pulse duration in experiments, where no COD has been detected. A borderline (gray) exists between two regions, i. e., parameter sets, of presence (orange) and absence of COD (blue). This borderline is somewhat blurred because of the randomness in filamentation of the laser nearfield and scatter in properties of the involved individual devices.

How does external feedback cause AlGaAs-based diode lasers to degrade?

“…The appearance of the resulting damage pattern is very similar to that observed in catastrophic optical (mirror) damage (CO(M)D). 4 In order to make sudden degradation less likely or even to avoid it, it is highly desirable to learn about the mechanisms, by which external feedback can trigger what eventually leads to CO(M)D. This represents the main goal of the present study. It relies on analysis of effects caused by gradual degradation in a diode laser that is subjected to accelerated aging under optical feedback.…”

Near-field dynamics of broad area diode laser at very high pump levels

“…However, under extremely high pumping, a further power increase can result in device failure via catastrophic optical damage (COD) of the laser facet. 6 COD is a sudden degradation mechanism. After reaching a critical temperature T crit of 120-160 • C, see Ref.…”

“…After reaching a critical temperature T crit of 120-160 • C, see Ref. 6, a small volume at the laser facet becomes highly absorbing for the laser light. This leads to a fast temperature rise at the COD site, the so-called thermal runaway, by transferring a part of the energy from the light field to the defect volume.…”

Near-field evolution in strongly pumped broad area diode lasers

“…This most likely represents the kinetics of thermal runaway as the fastest phase of the COD process, as described, e.g., in Ref. 6 Thereafter the lateral damage expansion continues with a constant velocity of (190±10) m/s for device B and (30±3) m/s for device C. Device C has been now subjected to another current pulse, and a velocity of (28±1) m/s is observed. This unchanged value shows that there is no significant reduction of the energy supporting the COD process.…”

“…At this threshold a critical temperature T crit of 120°C -160°C,see Ref. 6 , is reached in a small volume at the laser facet making this region highly absorbing for the laser light. This leads to a fast temperature rise by transferring energy from the light field to the damage site, called thermal runaway.…”