Donna Cunningham
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Carl Blesch
908-582-7474 (office) 908-306-0784(home)
[email protected]
BELL LABS DISTRIBUTED-FEEDBACK QUANTUM-CASCADE LASERS ADDITIONAL TECHNICAL INFORMATION
In a major technological breakthrough, Bell Labs researchers have demonstrated continuously tunable, single-mode, high-power room-temperature QC distributed-feedback lasers operating at mid-infrared wavelengths (5 and 8.5 micron) in pulsed mode. The single-mode tuning range is typically 50 nanometers in wavelength, and the peak powers are 60 milliwatts, one and two orders of magnitude better, respectively, than commercially available mid-infrared lead-salt lasers.
The lasersà high peak power, 50 milliwatts at 300 degrees Kelvin, allows the use of uncooled detectors and enables LIDAR (radar using light) applications. They are particularly well suited for portable, robust sensors in applications such as the point detection of trace gases and remote sensing applications.
QC lasers are made using molecular beam epitaxy (MBE), a materials-growth process from Bell Labs that makes it possible to build structures with layers only a few atoms thick. The QC laserÃs emission wavelength is determined initially by quantum-confinement effects: the fact that its layers are so thin ñ typically a few nanometers, or about 100 billionths of an inch ñ that electrons are squeezed and change their quantum-mechanical properties, allowing a range of possible wavelengths.
The distributed-feedback lasers incorporate a grating that makes it possible to further refine the laserÃs wavelength, making them continuously tunable.
QC lasers were invented at Bell Labs in 1994. Their operation is unlike that of all other laser. They operate like an electronic waterfall: When an electric current flows through a QC laser, electrons cascade down an energy staircase; every time they hit a step, they emit an infrared photon, or light pulse.
At each step, the electrons make a quantum jump between well defined energy levels. The emitted photons are reflected back and forth between built-in mirrors, stimulating other quantum jumps and the emission of other photons. This amplification process enables high output power.
Bell Labs has a long history of laser invention and innovation, beginning in 1958 with publication of the scientific paper describing the concept of the laser by Nobel Laureates Arthur Schawlow and Charles Townes. Both worked for Bell Labs at the time, Schawlow as a researcher and Townes as a consultant.
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Applications of Quantum Cascade Lasers
Important potential commercial applications of the QC laser -- based on the spectroscopic detection of molecular species ñ include environmental sensing and monitoring, with particular emphasis on pollution monitoring and measurement of air quality, in particular: ∑ remote sensing (over a range from hundreds of meters to a few miles) of chemicals such as toxic gases and vapors emanating from industrial smokestacks, landfills and other hazardous waste sites. ∑ point sensors, based on multipass absorption cells, of the local concentration of hazardous gases and vapors and short-range sensing (a few to tens of meters) for uses such as monitoring of automobile emissions on the entrance and exit ramps of highways, etc., combustion diagnostics via fast on-line monitoring of gases in automobile exhausts, collision avoidance radar, industrial process control, ammonia- and water-vapor sensing in agriculture to monitor dosages of fertilizer.
The enactment of the Clean Air Act Amendments (CAAA) of 1990 has resulted in a strong increase in these environmental monitoring needs. Most of the toxic chemicals (gases and vapors) included in the CAAA have strong absorption features in the 3-to-5-micron and 8-to-13-micron wavelength atmospheric transparency windows.
Other applications include ∑ medical diagnostics ∑ molecular clocks ∑ laser radar heterodyne detection.
Military applications include sensors for biological toxins and toxic gases such as nerve and mustard gas, countermeasures and infrared scene projection, treaty verification, etc. In the law enforcement area, the detection of explosives and of illicit drug production sites are among the possible uses.
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