High efficiency frequency stabilized tapered amplifiers with improved brightness

Semiconductor laser diodes with a tapered gain region provide a beam quality near to the diffraction limit combined with high output power. They can be configured as laser with a high-reflectivity coating on the rear facet as well as amplifier with an antireflection coating on both facets. In amplifier configuration they can be used in external cavity or MOPA - configuration with the advantage of a precisely tunable wavelength. Today amplifiers are commercially established with an optical output-power of 1-2W in a wide range of applications such as non linear spectroscopy and frequency doubling for blue-green outputs. Especially for the pumping of doped fiber amplifiers and materials processing higher power is requested. By extension of the resonator length from 2000μm up to 5000μm the output power of the amplifiers has been increased up to 10W at 976nm with beam quality near diffraction limit up to 8W. A wall-plug efficiency of more than 55% was reached in continuous wave operation. Improvements of the epitaxy structure and the mounting technology are essential for realizing longer resonators. Therefore an improved InGaAs/AlGaAs single quantum well vertical structure with low internal losses was grown by molecular beam epitaxy. The lateral design of the investigated devices consists of a ridge-waveguide section and a taper section with 4° taper angle. Due to the 4° taper angle the devices provide a small lateral far-field angle < 11° (95%).