Catastrophic degradation related to local heating in GaAlAs visible lasers occasionally occurs under relatively low optical output power. To develop highly reliable lasers, we used laser Raman spectroscope with an argon ion laser focused at about 1 μm≂ to evaluate the local operating temperature rise not only at the facet surface, but also along the striped active region. The local operating temperature rise in the vicinity of the facet’s active region increased exponentially up to 200 °C when the optical output power was 30 mW/facet. This high temperature causes the rapid formation of a dark region and final catastrophic degradation. The calculated temperature rise along the striped active region is about one-half of that of the facet. The internal operating temperature is far higher than the average temperature measured by the thermal resistance method, which is considered to be a large influence on the lifetime and activation energy of lasers in practical applications.

In order to realize the Johnson U BV and Kron-Cousins RI photometric systems in BFOSC, glass filters were purchased according to the Bessell prescription. All the filters are anti-reflection coated on both sides to increase the transmission. By comparing two dome flat-field exposures taken through any one of these filters set in two orientations 90 • apart, inhomogeneities in the filter transmission is clearly demonstrated. Using a PDS microphotometer, we have confirmed that the form of their spectral transmission curve varied from point to point on the filters. This kind of inhomogeneity cannot be eliminated by dividing by flat-fielding exposure and must be ascribed to inhomogeneities in the coating. This is not some accidental defect in coating, it is in the existing coating technique because all the filters (including the narrow-band interference ones) for the BFOSC and a Hβ filter made by another manufacturer showed a similar pattern. We found that for the studies of variable stars with amplitudes less than 0.05 mag. or studies aiming at establishing accurate C-M diagrams of star clusters, the usual uncoated Schott glass filters of Bessell's prescription are to be preferred.

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Available optical output powers from the Ga1−xAlxAs lasers are limited by the catastrophic optical damage or output power saturation due to local heating on the facet. Especially, the saturation of current-optical output power characteristically occurs during the operations at relatively low output power. This report describes the degradation process in an active region for lasers with the striped window as an electrode with respect to current-optical output power characteristics, electroluminescence image observation, and measurement of temperature rise at the facet and the cavity inside using laser Raman spectroscopy. The nonluminescing dark region observed in rapidly degraded lasers develops from the facet to the cavity inside. The dark region is so nonradiative that electron-hole recombination in that region produces heat rather than light. The measured local temperature on the facet drastically rises and the area influenced by local heating extends into the cavity inside. Although the threshold current increases by only 16%, the optical output power is saturated and finally the initial optical output power (20 mW/facet) is hardly maintained. It is found that the change in current-output power characteristics almost corresponds to the calculated results which incorporated temperture dependence of local absorption loss in the dark region.

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