NRL Develops New Semiconductor Quantum Well Lasers

6/22/1998 - 29-98r
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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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