Semiconductor laser with 8 W optical output power is world's first

Regensburg, Germany | 6 February 2003 -- Osram Opto Semiconductors has announced its first prototype of an optical pumped semiconductor (OPS) disk laser. The developers achieved an optical output power of 8 W with an optical pump power of 19 W at a wavelength of 980 nm.

Compact, powerful, and cost-effective laser light sources in red, green, and blue are essential if the dream of laser TV, as well as numerous other applications, is to become reality. As part of the MISTRAL (miniaturized radiation sources) 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 master oscillator power amplifier (MOPA) and the OPS disk laser -- the disk laser concept emerged as the clear favorite. 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.

OPS semiconductor lasers have the potential to overcome the limitations of high-power semiconductor lasers and therefore to supercede solid-state lasers in various areas. The main factors contributing to this enormous improvement in terms of power output are the carefully chosen quality of the semiconductor material, the design, and the effective dissipation of excess energy away from the active area of the laser. In addition to the perfectly round, high-quality beam, a further key advantage of OPS disk lasers is that the power output can be scaled up or down via the pump spot diameter.

Due to limited beam quality of available high-power edge emitting semiconductor broad-area lasers, they are used primarily for optical pumping of solid state lasers (beam converter). The improved beam quality of tapered laser bars and stacks, for example, enables a better focusing on the work piece on kW power levels and can be applied to a wide field of industrial applications. Unfortunately, most semiconductor laser concepts with further improved beam quality (M2<2) are restricted in optical output power. The OPS disk laser overcomes this power limitations.

The semiconductor material of the OPS disk lasers consists of an active layer of quantum films that generate the light and an integrated, high-quality semiconductor reflector. The OPS disk laser resonator is formed by the semiconductor structure and an external out-coupling mirror. The latter is partially transparent for the laser beam and couples a part of the laser light out of the cavity. Finally, an intra-cavity frequency doubling process using non-linear optical crystals (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.

The power output of OPS disk lasers can be scaled up or down in a similar fashion to solid-state lasers. The round profile of the beam and the high quality of the beam mean that the laser can be focused extremely well on the work piece. Semiconductor disk lasers could for example replace marking lasers based on solid-state lasers. Inscriptions and engravings, but also welding, drilling, and cutting can all be performed far more cost-effectively with semiconductor lasers. Other conceivable applications are energy and data transfer, use in automotive applications and in printing and medical technology.

At the moment, laser projectors are still in the realm of high-end applications, for example in planetariums, cinemas, or flight simulators. These applications use high-performance solid-state lasers, which, due to their size, their high consumption of electricity and cooling water and, significantly, their high price, cannot be used in more broad-based applications. Thanks to the powerful semiconductor lasers, laser projection for normal end users in the form of laser TV is now a real possibility for the future. The advantages are clear: any shade of any color can be generated by mixing the three complementary colors red, green, blue, and even white. Black is created by masking the three colors. Laser beams produce excellent image definition and generate a picture that is virtually free of flickering and has bright, natural colors. The excellent definition of the image with quasi infinite depth of field means that the picture can be projected on to any kind of surface, consigning generations of TVs to history.

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