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- Thermography (4)
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- High-power diode lasers (3)
- Non-destructive testing (3)
- Semiconductor laser (3)
- Carrier density (2)
- Destructive testing (2)
- Auger effect (1)
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Catastrophic optical damage (COD) is analyzed during single current pulse excitation of 975 nm emitting diode lasers. Power transients and thermal images are monitored during each pulse. The COD process is unambiguously related to the occurrence of a thermal flash of Plancks radiation. We observe COD to ignite multiple times in subsequent pulses. Thermography allows for tracing a spatial motion of the COD site on the front facet of the devices. The time constant of power decay after the onset of COD has values from 400 to 2000 ns, i.e., an order of magnitude longer than observed for shorter-wavelength devices.
Single-pulse tests of the catastrophic optical damage (COD) are performed for three batches of diode lasers with different gain-regions. The tests involve in situ inspection of front, rear, and side of the devices by a thermocamera. Devices with an Al-containing gain-region show COD at the front facet, as expected for strong facet heating via surface recombination and reabsorption of laser light. In contrast, Al-free devices with low surface recombination rates tend to fail at the rear facet, pointing to a different heating scenario. The high carrier density at the rear facet favors heating and COD via Auger recombination processes.
Double-side cooled high-power diode laser bars packaged by different techniques on different types of passive heat sinks are analyzed in terms of packaging-induced strain. Reference data from standard devices being single-side cooled only and packaged by conventional soft and hard soldering are also presented. Thermal profiling across the devices complements the results. The most suitable packaging architecture and technique for double-side cooled bars is identified. Measurements of the laser emission near field and electroluminescence pattern provide direct reference to the functionality of the devices. Furthermore, a type of cross calibration of the methods used for strain analysis is made, since all techniques are applied to the same set of bars. This involves micro photoluminescence, micro Raman, and degree-of-polarization electroluminescence spectroscopy.
Mechanisms and fast kinetics of the catastrophic optical damage (COD) in GaAs-based diode lasers
(2011)
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.
The spontaneous emission of a GaAs-based tapered laser diode emitting at λ = 1060 nm was measured through a window in the transparent substrate in order to study the carrier density distribution inside the device. It is shown that the tapered geometry is responsible for nonuniform amplification of the spontaneous/stimulated emission which in turn influences the spatial distribution of the carriers starting from below threshold. The carrier density does not clamp at the lasing threshold and above it the device shows lateral spatial hole-burning caused by high stimulated emission along the cavity center.