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Osram backs laser television development

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Osram Australia has brought the laser television a step closer with the first Optical Pumped Semiconductor (OPS) disk laser prototype to achieve an 8 W optical output power with an optical pumping power of 19 W at a wavelength of 980 nanometers (nm).

The development falls under the miniaturised radiation sources (MISTRAL) research project, Osram Opto Semiconductors is developing semiconductor lasers with high optical output power, good beam quality and long lifetimes.

The project has been running since June 2000 and is partly funded by the German Federal Ministry of Education and Research. After evaluating two laser concepts, the short-pulse MOPA concept and the OPS disk laser concept, the disk laser concept 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 1300 nm, but they can also be operated as lasers in the red wavelength range.
This means that OPS semiconductor lasers have the potential to overcome the limitations of high-power semiconductor lasers, therefore superseding solid-state lasers in various areas.

The main factors contributing to this enormous power-output improvement are the carefully chosen quality of the semiconductor material, the design and the effective dissipation of excess energy away from the laser's 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.Current applications are predominately high-end, including planetariums, cinemas and flight simulators, although the OPS breakthrough will make laser projection for normal end users in the form of laser televisions a reality in the near future.

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