Comparison of concepts for high-brightness diode lasers at 976 nm

Abstract

Especially for fiber pump applications there is a strong demand for high-brightness diode lasers in the 10W power regime. Broad-area and tapered laser concepts seem to be the most promising candidates for high brightness, which is proportional to output power divided by beam quality. Within this talk we give a comparison of both concepts identifying the possibilities and limitations of both concepts. Whereas fast axis far fields show mostly a current independent behaviour, for broad-area lasers near- and farfields in the slow axis suffer from a strong current and temperature dependence, limiting the brightness. For tapered diode lasers the brightness is limited by the temperature characteristics of M² and astigmatism. Therefore for both concepts it is essential to have lasers with excellent thermal management, which can be realized by 4- 5mm long resonators in combination with wall-plug efficiencies well beyond 60%. To fulfill these issues, we have realized MBE grown InGaAs/AlGaAs broad-area and tapered lasers with resonator lengths between 4mm and 5mm and 45° fast axis far field emitting at 976nm. For a 5mm long broadarea laser with 90μm stripe width a beam parameter product of less than 5.9 mm x mrad (M²<10) has been achieved at 10W with a slope efficiency of 1.1W/A and a maximum wall-plug efficiency of 65%. For a tapered laser with a taper angle of 4° and 5mm resonator length, 10W have been demonstrated with a slope efficiency of 1.05W/A and a maximum wall-plug efficiency of 56%. Beam quality is below 3 up to 8W.