Researchers at the Naval Research
Laboratory's (NRL's) Optical Science Division have developed
several new types of semiconductor lasers that emit light in
the "mid-wave infrared" spectral region (light at wavelengths
between 3 and 5 microns). The new lasers are suitable for use
in both military and civilian applications.
Applications include: chemical
sensing (for leak detection, monitoring of atmospheric pollution,
chemical weapons, drugs, etc.), protection against heat-seeking
missiles, laser surgery, laser radar, and infrared (IR) scene
projection.
Drs. Jerry Meyer, Igor Vurgaftman,
Chris Felix, Filbert Bartoli, Jr., Bill Bewley, Ed Aifer and
Linda O1afsen, of the Optical Physics Branch, and Lew Goldberg,
of the Optical Techniques Branch, comprise the research team.
This work is funded by the Office of Naval Research (ONR).
According to Dr. Meyer, "Over
half of all U.S. aircraft losses in combat are caused by heat
seeking missiles. The semiconductor lasers we have developed
are of great importance to the military as a way to meet this
threat. These lasers will be a convenient high-powered light
source that operate at 3-5 micron wavelengths making them suitable
for this application. There are currently no lightweight, high-power
light sources available at these wavelengths that operate at
room temperature."
The research team has used an
advanced design capability called "wavefunction engineering"
that has enabled them to design and model complex layered quantum
well structures. All of the structures have been based on the
antimonide family of III-V semiconductors from which quantum
wells were grown by molecular beam epitaxy (MBE) at the University
of Houston, Sarnoff Corporation, Hughes Research Laboratory,
or NRL's Electronics Science and Technology Division. One example
of this is the "W" laser in which a gallium indium
antimonide (GaInSb) hole quantum well is surrounded on both sides
by two indium arsenide (InAs) electron quantum wells and aluminum
antimonide (AlSb) quantum barriers. This serves to maximize the
optical gain while suppressing the power lossesinside the
device.
An NRL developed optically-pumped
W laser was the first interband mid-IR laser to operate at room
temperature. A W laser also currently holds the record for maximum
continuous-wave (cw) operating temperature (-53 degrees C) for
all III-V mid-IR lasers.
Another new approach that NRL
has played a leading role in developing is the interband cascade
laser (ICL). The ICL produces a cascade of photons as electrons
descend a potential staircase and emit an additional photon at
each step. The research team reports it has recently achieved
the pulsed operation of a 3.5-um ICL with a W active region to
temperatures as high as 13 degrees C, which is nearly room temperature
and is more than 60 degrees higher than the best temperature
for any earlier interband III-V laser emitting at such a long
wavelength. Room temperature operation will be very important
if mid-IR lasers are to find extensive use in a broad range of
environments.
A third structure recently designed
and tested at NRL is the first III-V mid-IR vertical-cavity surface
emitting laser (VCSEL). This optically-pumped laser with a W
active region operated nearly to room temperature (7 degrees
C for pulsed operation. In VCSELs, light is emitted from the
top of the device rather than the side, and the active volume
can be extremely small. For this reason the cw pumping threshold
(power at which the laser could be turned on) for the NRL VCSEL
at low temperatures was only 4 milliwatts (mW), which is far
smaller than for any earlier mid-IR semiconductor laser.
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