Optical Pumping For High Power Laser
This clearly exceeds previously documented power and efficiency maximum values, says Osram. The company is looking to use laser projection in wide consumer applications such as laser televisions. Compact, powerful and cost-effective laser light sources in the colours red, green and blue are essential to the implementation of a laser television.
Osram Opto Semiconductors is working to develop semiconductor lasers with high optical output power, good beam quality and long lifetimes as part of the miniaturized radiation sources (MISTRAL) research project. This project has been running since June 2000 and is partly funded by the German Federal Ministry of Education and Research.
The research evaluated two techniques, the short-pulse MOPA (master oscillator power amplifier) and OPS disk lasers. The disk laser emerged as the clear favourite.
Depending on the material system, OPS disk lasers can not only emit in the infrared range at wavelengths between around 900 and 1300nm, but can also be operated in the red wavelength range.
The main factors contributing to the power-output improvement are the carefully chosen quality of the semiconductor material, the design and the effective dissipation of excess energy away from the lasers active area. In addition to the perfectly round, high-quality beam, a further key OPS disk laser advantage is that the power output can be scaled up or down via the pump spot diameter.
The previously available edge-emitting, high-power semiconductor lasers have only a limited beam quality and are only suitable for optical pumping of solid-state lasers (beam converters). Alternative semiconductor laser concepts with better beam quality have failed because the output was limited to just a few watts.
The semiconductor material of the OPS disk lasers consists of an active layer of quantum films, which generate the light, and an integrated, high-quality semiconductor reflector. A part of the infrared laser beam is then decoupled via a second, semi-permeable external resonator mirror. Finally, a frequency-doubling process using non-linear optical (NLO) crystals is used to convert the invisible infrared beam into visible light. In this process, two infrared photons are converted into a single photon with twice the energy in the visible range of the spectrum. In this type of application the external resonator mirror reflects the infrared laser beam but allows the visible, frequency-converted laser beam through.
