A portable, shoe-box-sized chemical detector

To craft their new laser, the team started with a standard laser diode, similar to those in laser pointers and barcode scanners. This pulse was then boosted in power with telecom amplifiers—similar to those used in the field to periodically ramp voice signals backup as they diminish over long travels through the fiber-optic lines. Then they ran this powerful, broadband signal through a 2-meter coil of optical fiber.

“This is where the magic comes in,” said Islam. “We put in these roughly one-nanosecond pulses at this high power and they break up into very narrow series of small short pulses, typically less than a picosecond in width. So basically for the price of 20 cents of fiber, we obtain the same kind of output as very expensive mode-locked lasers.”

Then, in a process known as “supercontinuum generation,” they expanded the wavelengths covered by that light by sending it through specialized softer glass fibers. Most lasers emit light of just one wavelength, or color. But supercontinuum lasers give off a focused beam packed with light from a much broader range of wavelengths.

Visible-wavelength supercontinuum lasers, for example, discharge tight columns that appear white because they contain light from across the visible spectrum. Islam’s broadband infrared supercontinuum laser does the equivalent, but in longer infrared wavelengths.

To use the device, the researchers shine the laser on an object and analyze the reflected light to identify what wavelengths did not bounce back. They can identify chemicals by the unique pattern of infrared wavelengths that they absorb.

U_M says that the team successfully demonstrated the laser for the U.S. Intelligence Advanced Research Projects Activity in August 2017, analyzing 70 mystery samples over two days of testing. Phase 2 of the project will entail shrinking the system toward the size of a shoebox, a process that will be led by Leidos and Omni Sciences.

In addition to the applications in policing and defense, Islam sees a future for the technology in medicine. For instance, tissue samples are chemically analyzed in a laboratory—a process that takes time and materials. Islam thinks the laser could provide an assessment of the chemical content on the spot. It may even be possible to run the beam through a scope and analyze tissue right in the body.

— Read more in Mohammed Islam et al., “Mid-infrared supercontinuum generation from 1.6 to >11 micrometers using concatenated step-index fluoride and chalcogenide fibers,” Optics Letters 42, no. 24 (15 December 2017)