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High-power high-brightness ridge-waveguide tapered diode lasers at 940 nm
Hochleistungs-Trapez-Diodenlaser hoher Brillanz mit Rippenwellenleiterstruktur bei 940 nm
Semiconductor lasers with high beam quality and high optical output power are very attractive for a variety of applications such as optical pumping of solid-state lasers, fiber amplifiers and medical treatment. When easy and low-cost fabrication is a further requirement, devices based on tapered gain sections are the most promising candidates. Low model gain, single quantum well InGaAs/AlGaAs devices emitting at 940 nm were grown by molecular beam epitaxy. The lateral design consists of a tapered gain guided and a ridge-waveguide section having an overall length between 2 mm and 3 mm. Whereas the length of the tapered structure determines the high output power, the high brightness requires a ridge-waveguide structure with sufficient length. Here the length of the ridge section has been chosen to 500 µm. We achieved an optical output power of up to 5.3 W at room temperature in continuous wave mode. The threshold current density depends on the tapered length with values between200 A/cm2 and 650 A/cm2. The slope efficiency is around 0.9 W/A for all devices. The wall plug efficiency reaches 44 % at a current of 3 A. The beam quality factor remains nearly constant up to about 2.2 W having an M2-value of 1.3. At higher optical output powers M2 increases fast. The lifetime of such devices has been extrapolated to more than 7500 h at room temperature.