808 nm high power diode laser stack with polarization coupling

High-power diode lasers based on GaAs semiconductor bars meanwhile are well established as reliable and highly efficient laser sources. Continuous improvement of the semiconductor material itself as well as mounting and cooling techniques during the last years have led to increased output power and high lifetimes. In many cases high power diode lasers are on the way to replace flashtubes for solid state laser pumping. By realizing arrangements of many high-power diode laser elements, e. g. diode laser stacks, the overall output power can be increased further up to the kW range. In this power level, we can have many important applications, such as surgery, welding of polymers, soldering, coatings and surface treatment of metals. But there are some applications, which require much higher power and brightness, e. g. hardening, key hole welding, cutting and metal welding. In addition, high power diode lasers in the military also have important applications. So all developed countries have attached great importance to high-power diode laser system and its applications. Germany is developing initiative "BRIOLAS" ( brilliant diode lasers) program, the German Federal Ministry of Education and Research (BMBF) is supporting the BRIOLAS-initiative with about 30 M∈. The United States have launched "SHEDS" (High Efficiency Diode Sources) from 2005. Now Germany laserline corporation have products, that direct diode laser system have largest output power of 10 000 W, and fiber coupled diode laser system have largest output power of 8 000 W into the 1.5 mm diameter of the fiber. We know that under certain circumstances the light, which is emitted from the diode laser bar is linearly polarized, and the polarization degree can be 95 %-98 %. So polarization coupling technology makes two laser beam of perpendicular polarization direction reciprocally together, that is another effective way to improve the power and the brightness of diode lasers. After fast axis collimating, the polarization direction of one laser stack is rotated 90° through a half-wave plate, thus, the polarization directions of two laser stack are vertical reciprocally. The beams of two lasers are incident to polarization filter; one transmits through it, and the other is bent on it. Finally two beams combine to one. In this paper, it mainly introduces the principle of polarization coupling, technique route, experiment result and analysis. The polarization coupling efficiency can achieve 90% for two LD stacks with seven bars whose emission wavelength is 808 nm. The efficiency of 67% can be achieved after focusing to the beam size of 4.5 mm × 4.5 mm.