Semiconductor Disk Laser
semiconductor (OPS) disk laser prototype. The company says that for the
first time its developers have achieved an 8W optical output power with an
optical pumping power of 19W at a wavelength of 980nm. This 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 would be needed for such an
implementation. The current development provides the red component.
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,
one based on a short-pulse MOPA (master oscillator power amplifier)
arrangement and the other on OPS disk lasers. The disk laser emerged as the
clear favourite.
Depending on the material system, OPS disk lasers 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
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 to deliver more than a few
watts of output power.
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-reflecting 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.
Other possible applications include laser marking, etching, welding,
drilling, cutting and energy and data transfer.
