Chemical detector This laser is used to optically "heat" very small particles. U.S. Army Research Laboratory

A new system to detect chemical warfare attacks can identify incredibly low levels of dangerous toxins in the air by their sound.

The new technique can detect multiple dangerous chemicals in the air using a phenomenon called the photoacoustic effect, which is when materials generate specific sound waves when they absorb light. Researchers use lasers as the light source and very sensitive microphones to pick up the sounds that chemicals make.

With this system researchers could detect tiny amounts of gasses, down to parts per trillion levels. The problem? They could only scan for one compound at a time.

Kristan gurton Dr. Kristan Gurton, an experimental physicist in the Battlefield Environmental Division, Computational and Information Sciences Directorate, US Army Research Laboratory, conducts experiments. U.S. Army Research Laboratory.

"Photoacoustics is an excellent analytic tool, but is somewhat limited in the sense that one traditionally only measures one absorption parameter at a time," says Kristan Gurton, an experimental physicist at the U.S. Army Research Laboratory in Adelphi, Md, said in a statement from the Optical Society of America. 

Instead of using traditional photoacoustic set ups, Gurton created a sensor that can detect the different sounds put off by multiple different chemical weapons when they are struck with six different lasers. Each laser has a different effect when it hits the molecules of gas, creating a distinct set of sounds for each chemical.

"Different agents will affect the relative 'loudness' of each tone," Gurton said, "so for one gas, some tones will be louder than others, and it is these differences that allow for species identification." The work will be published in the August 15 issue of the journal Optics Letters.

gas detector A device based on selective real-time detection of gaseous nerve agent stimulants using multi-wavelength photoacoustics could look like this, in which now "multiple" lasers are used. U.S. Army Research Laboratory

Ultimately the method "could be tailored for a variety of detection scenarios ranging from the obvious need to protect our soldiers during conflict to civilian applications like detecting the presence of harmful chemical gases that are difficult to detect with conventional techniques," Gurton says.

The technology is surprisingly portable, it could be shrunk down to the size of a milk carton for soldiers to carry with them. "A photoacoustic cell is surprisingly simple and inexpensive to produce," Gurton adds.