August 25, 2012
Northwestern Develops Improved Standoff Sensing Laser
redOrbit Staff & Wire Reports — Your Universe Online
Manijeh Razeghi, a Professor of Electrical Engineering and Computer Science in the university's McCormick School of Engineering and Applied Science, and colleagues have crafted a new resonator that they believe will produce improved single-mode quantum cascade lasers at the 8-12 micron range.
Stronger, higher quality lasers at that wavelength will make it easier for military personnel, law enforcement, and industrial workers to better detect gas, explosive material, or other hazards at a greater distance, the researchers announced in a Thursday press release.
"Infrared radiation in the 8-12 micron range is of interest for military and industrial use equally, as almost all chemicals (including nerve gases and toxic industrial chemicals) can be identified by infrared absorption in this range," the university said in that statement. "In addition, the atmosphere is relatively transparent in this wavelength range, which allows for sensing from a distance."
"But to be successful, standoff sensing applications require that laser sources be high-powered, single-mode, and possess good beam quality. Incorporating all three qualities in a single device is a significant challenge, and many sophisticated structures have been proposed with little success," they added.
As part of their research, which has been published in the August 21 edition of the journal Applied Physics Letters but has not yet been directly funded, Razeghi's team utilized a brand new type of "distributed feedback" mechanism that makes it possible to control both the wavelength and beam quality of the laser. They are calling the mechanism B-DFB, noting that it offers simple diffractive feedback in an angled laser cavity.
"Our resonator is the most promising device for creating high-power, single-mode laser sources with good beam quality, and it is inexpensive and can be realized at room temperature," Razeghi said in a statement. "Furthermore the design can be applied to a wide range of semiconductor lasers at any wavelength."
"Razeghi and her group demonstrated >6 watts of peak power with nearly diffraction-limited beam quality at a wavelength of 10.4 microns -- the highest power single-mode semiconductor laser demonstrated at a wavelength greater than 10 microns," the university added. "Refinement of the design, particularly related to optimization of the laser cavity design and improvement of the gain medium, are expected to increase the output power significantly."