Temperature distribution study of Al-free diode lasers by photothermal techniques

There is an increasing interest in Al-free 980 nm lasers, (1-3) due to advantages over InGaAs/AlGaAs lasers: significantly lower electrical and thermal resistance(2,3) and their potential for improved reliability. The Wallplug efficiency of such a lasers is the highest reported up to now (4). In order to improve the reliability of such lasers at output powers near the catastrophic optical damage (COD) limit it is increasingly important to identify and analyse the causes of degradation mechanisms during laser operation. Special attentions is addressed to localizing and identifying the heat sources near the laser diode facets. The structure of the investigated laser diodes is described in (4), the main difference from the traditional laser diodes is that here was applied the large-optical-cavity concept (5), according to which the waveguide consists of a relatively wide (0.6 mu m) layer of InGaAsP with a strained double quantum well in the center. The cladding layers are InGaP lattice matched to GaAs. In such a laser structure it is possible to obtain an internal optical loss coefficient as low as 2 cm(-1). The mirror temperature (T-m) estimation is therefore extremely important in order to predict the degradation rate of these high performance lasers.