Christian Hanke

Highly reliable 40-W cw InGaAlAs/GaAs 808-nm laser bars

The fundamental question whether aluminum-free semiconductor lasers in the 808 nm band are significantly more reliable than Al-containing lasers is still open. We have fabricated and tested high-power InGaAlAs/GaAs-lasers which show excellent reliability data at and above 40 W cw. The laser structure consists of an InGaAlAs-double-quantum well (DQW) as active layer embedded in a large optical cavity (LOC) waveguide structure. The layers were grown in a low pressure MOVPE (LP- MOVPE) reactor using high quality precursors. Asymmetrically coated bars with a width of 1 cm containing 25 groups of 200 micrometer wide emitters were mounted junction down on actively cooled heatsinks. At a heatsink temperature of 18 degrees Celsius the slope-efficiency is 1.1 - 1.2 W/A. Due to the low series-resistance of 2.2 m(Omega) and the low internal losses in the range of 1.7 cm-1 the overall efficiency at 40 W cw reaches 50%. Lifetime studies over 33 0000 h accumulated device hours show that the laser bars with a resonator length of 900 micrometer can be operated at 40 W with high reliability. The mean degradation rate is -0.11%/kh. This result emphasizes that Al-containing lasers can also have a very high reliability usually claimed for Al-free lasers. As a consequence of these encouraging results we will start further lifetime tests at 50 to 60 W.

High Power Diode Lasers

The unique features of semiconductor laser diodes open a wide field of applications. The high power capability of these devices in combination with high efficiency, small volume, a wide range of available wavelengths and the cost reduction by mass production are the main factors for the increasing use of laser diodes. The purpose of this article is to give an overview of the recent developments in the field of high power laser diodes. The scope is from single stripe lasers with diffraction limited beams to stacked laser arrays with kW-power capability.