MURRAY HILL, N.J., Feb. 20 (UPI) -- A new super-continuum infrared laser on a microchip from Bell Labs can perform the work of a dozen other lasers, researchers said Wednesday.
"It's a bunch of lasers stacked together, but in the end, they only have the size of one laser," said lead researcher Claire Gmachl of Bell Labs in Murray Hill.
The laser may soon help detect airborne toxins in spacecraft and nerve gases or explosives for public safety, as well as photographing molecules no one could see properly before. Scientists add the laser may one day be able to transmit communication wavelengths for super-fast data transmission.
"The realization of an ultra-broadband quantum cascade laser is a breakthrough," commented electronics scientist Karl Unterrainer of the Technical University of Vienna.
Most lasers are narrowband -- they emit only one wavelength, only one color from light's broad palette. There are several different kinds of broadband lasers, but each is technologically complex or unable to emit a constant beam.
The new laser can fire infrared wavelengths over a wide range with none of the drawbacks of previous broadband lasers. It does so using "quantum wells" -- crystalline layers of semiconductors thinner than a wavelength of light.
These delicate films -- each only nanometers or billionths of a meter thick -- are sandwiched together and have varying electrical conductivities. When electricity charges the quantum wells, electrons remain confined together between the more electrically resistant layers to increase each other's energy levels and emit bright light.
By sandwiching atop each other 650 quantum wells of varying widths -- in total a stack still 50 times thinner than a human hair -- the scientists created a "quantum cascade" effect. Each quantum well emits different wavelengths of light because of their different thickness, and each film is stacked in a way that makes them unite to generate laser activity.
"They all work together, so none of them really has to work so hard to become a laser," Gmachl told United Press International. "It has exactly the peak power of a regular laser, but it gives you a whole spectrum."
The super-continuum laser -- which fits on a single microchip -- is able to emit many infrared wavelengths simultaneously. In practice, scientists can tune it to emit one laser wavelength at a time. This makes the laser ideal as an advanced scanner.
"An ultra-broadband band laser allows the development of a system which is very universal -- that is, it could cover many substances in gaseous, solid or liquid form." Unterrainer said.
The researchers also are looking at making a broadband laser that emits communication wavelengths at trillions of bits per second. Finding the right chemical mix for quantum wells there will not be easy, though.
"It's a tough material challenge -- five to 10 years is a reasonable timeframe for such things," Gmachl cautioned.
Immediate applications include detectors of trace gases such as carbon monoxide and other environmental pollutants, which absorb infrared light.
"NASA has identified about 50 primary and secondary potential toxic gases that need monitoring for extended spaceflight by humans. The ability to detect and monitor these gases would be greatly aided by greatly tunable broadband quantum cascade lasers," said physicist Frank Tittel of Rice University in Houston. He added "the ability to look for nerve gases and explosives could aid law enforcement and public safety."
The laser also could easily generate super-brief laser pulses only a million billionths of a second long, to essentially take flash photos of molecular reactions as they happen.
"The generation of such short laser pulses was so far almost only possible with optically pumped solid state lasers ... these are expensive table-top systems and cannot be integrated in one chip, limiting their broad technical implementation," Unterrainer explained. "The quantum cascade laser could take advantage of all the attractive features of ultra-fast solid state lasers and open a large market."
The researchers reported their findings in the scientific journal Nature.
(Reported by Charles Choi in New York.)
