Researchers from the University of Michigan have designed a chemical sensor prototype with the potential to detect “single-fingerprint quantities” of substances from a distance of over 100 feet. They are now striving to reduce its size to that of a shoebox.
It could possibly be used to detect traces of explosives and drugs, and also for accelerating the investigation of specific medical samples. A portable infrared chemical sensor can be installed on a drone or carried by users such as border officials, doctors, soldiers, and police.
The sensor is rendered made possible by an innovative optical-fiber-based laser that integrates high power with a beam that covers a wide band of infrared frequencies (1.6-12 mm), covering the commonly known mid-wave and long-wave infrared.
Most chemicals have fingerprint signatures between about 2 and 11 microns, hence, this wavelength range is called the ‘spectral fingerprint region’. So our device enables identification of solid, liquid and gas targets based on their chemical signature.
Mohammed Islam, University of Michigan researcher who designed the laser.
The project is a partnership between University of Michigan; Leidos, a global technology company; IRflex and CorActive, fiber makers; and Omni Sciences, a University of Michigan startup which was founded by Islam. The U.S. Intelligence Advanced Research Projects Activity funded the study.
University of Michigan professor of electrical and computer engineering and biomedical engineering Islam and his colleagues developed their device by using prefabricated fiber optics and telecommunications components, other than one tailor-made optical fiber. This strategy makes sure that the laser is dependable and functional to produce at a reasonable price.
“We’ve shown we can make a $10,000 laser that can do everything a $60,000 laser can do,” stated Islam.
Broadband infrared lasers are generally developed by using a laser that generates very short light pulses, following which a series of amplifiers increase the power. However, this strategy is restricted to use in labs. Apart from their higher costs, the size of these components cannot be reduced to a small enough size to be compact for a handheld device. In addition, the use of mirrors and lenses will render the device sensitive to push and pull as well as alterations in temperature.
In order to develop this innovative laser, the researchers used a standard laser diode similar to the one used in barcode scanners and laser pointers. Then, telecom amplifiers were used to boost the power of the pulse, where the amplifiers were similar to the ones used in the field to periodically ramp up backup for voice signals when they get diminished over long paths through the fiber-optic lines. Subsequently, they conveyed this ramped up broadband signal through a 2-m optical fiber coil.
“This is where the magic comes in,” stated 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.”
Following this, via a process called “supercontinuum generation,” the researchers expanded the wavelengths that the light covered, by sending it through specialized, soft glass fibers. The majority of the lasers discharge light of only one color or one wavelength. In contrast, supercontinuum lasers emit a focused light beam including light of a very wide array of wavelengths.
For instance, visible-wavelength supercontinuum lasers emit tight columns that seem to be white as they include light from across the visible spectrum. The broadband infrared supercontinuum laser developed by Islam works very similarly, but at longer infrared wavelengths.
In order to use the device, the team focused the laser on an object and investigated the reflected light to ascertain the wavelengths that did not rebound. The chemicals can be identified by the distinctive infrared wavelength pattern absorbed by them.
The researchers were successful in demonstrating the laser for the U.S. Intelligence Advanced Research Projects Activity in August 2017, investigating 70 unknown samples over 2 days of investigation. Phase 2 of the study will focus on minimizing the size of the system equal to that of a shoebox—a research that will be headed by Leidos and Omni Sciences.
Apart from applications in defense and policing, Islam hopes the technology will be used in medicine in future. For example, tissue samples are chemically tested in a lab, which involves considerable time and materials. Islam believes that the laser can enable on-the-spot investigation of the chemical content. It might be even feasible to focus the beam through a scope and investigate tissue right in the body.
The features of the laser have been detailed in an article titled “Mid-infrared supercontinuum generation from 1.6 to >11 micrometers using concatenated step-index fluoride and chalcogenide fibers” published in the Optics Letters journal.