nitride lasers technology
rhombus4
Stretching from the blue to the green
Osram has been a front-runner in race to make a green-emitting nitride laser, and its
attempts to reduce dark spots in the active layer have enabled the company to be the first to
break the 500 nm barrier. Stephan Lutgen, Uwe Strauß and Michael Schmitt detail
device development and the wide variety of applications that promise to benefit from it.
G
Research
reen lasers can serve many applications. engineers at
Thanks to an emission wavelength that is Osram Opto
close to the peak sensitivity of the human eye, they are Semiconductors
ideal for aiding positioning and leveling tasks in the have recently
construction industry. If they are united with red and blue developed a
sources, they can form full color projectors that can form series of green
an image on a screen. And they can also be used for InGaN laser
medical treatments, such as addressing a common form diodes that
of blindness. emits at
wavelengths up
The ideal laser for all these tasks is a single, small to 526 nm
compound semiconductor chip. These are not
commercially available today, but lasers based on the
nitride family of materials have recently reached these (Nd:YVO
4
) lasers. Both operate by employing a 808 nm
wavelengths, and they promise to combine a very stable GaAs-based laser diode to optically pump a 1060 nm
output over a wide temperature range with fast solid-state laser, and then frequency doubling the
modulation speeds and high efficiency. These attractive emission produced by this laser to 530 nm with a non-
attributes have driven the development of longer linear optical up-conversion process, using lithium niobate
wavelength nitride lasers for many years: the 405 nm (LiNbO
3
), lithium triborate (LiB
3
O
5
), or similar crystals.
lasers that are employed in BluRay players and recorders
were commercialized in 2000; and chipmakers were If the temperature of the pump diode shifts, its emission
selling 440-460 nm lasers by the middle of that decade. wavelength changes considerably. This is highly
However, further commercial progress has been undesirable because the solid-state laser has a narrow
incremental, and the longest wavelength nitride laser that absorption range, and this in turn restricts its operating
can be ordered from a manufacturer emits at 488nm [1]. temperature, which can be increased through the costly
addition of external stabilization. To make matters worse,
Commercial limits there is a strong intensity noise issue that can require
If commercial nitride lasers can be extended to the green, additional elements within or outside the laser cavity for
they could replace the far more cumbersome designs that stabilization. Another downside of this type of laser is that
are currently in use. These are either based on diode- its modulation speed is limited to the kHz range, due to
pumped solid-state lasers, or frequency-doubled the long lifetime of the charge carriers, and this means
semiconductor lasers. Regardless of what approach is that the diode-pumped solid-state laser cannot be
used, these commercial offerings tend to be complex deployed for scanning beam projectors without an
systems requiring additional electronics and optics for additional external modulator. However, in its very simple
stabilization within a reasonably broad operating range. configuration this type of lasers can be used as a laser
pointer, and more complex versions delivering a stable
Two common examples of the diode-pumped solid-state output power can serve medical and bio-technical
laser are neodymium-doped yttrium aluminum garnet applications. And by increasing the output power, these
(Nd:YAG) and neodymium-doped yttrium orthovanadate emitters can also be used in laser shows.
January/February 2010
www.compoundsemiconductor.net 21
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