Degradation mechanism and the related change in lasing characteristics for a mirror degradation were investigated in AlGaAs doublehyphen;heterostructure lasers with uncoated mirror surfaces. In constant opticalhyphen;power operation, mirror degradation was classified into three phases. The lasinghyphen;characteristics degradation in the initial stage of phase I was well explained in the excitationhyphen;enhanced oxidation model. Darkhyphen;line defects, originating from mirror surfaces, were found in the final stage of phase III, following phase II with a low degradation rate. The mechanism of the opticalhyphen;power dependence was also investigated. Marked improvement in operating life was confirmed by the dielectric film coating and in a newhyphen;structure laser with little excitation in the vicinity of mirror surfaces.
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