Laser sniffs out toxic gases from afar

This powerful one-ton laser, capable of firing dozens of pulses a second, gives researchers a new way to detect tiny amounts of hazardous gases from up to one kilometer away, and under normal atmospheric pressure -- something that wasn't thought possible before. Credit: Henry Everitt, U.S. Army and Duke University.

 http://phys.org/news/2014-12-laser-toxic-gases-afar.html#jCp

Scientists have developed a way to sniff out tiny amounts of toxic gases—a whiff of nerve gas, for example, or a hint of a chemical spill—from up to one kilometer away.

The new technology can discriminate one type of gas from another with greater specificity than most remote sensors—even in complex mixtures of similar chemicals—and under normal atmospheric pressure, something that wasn't thought possible before.

The researchers say the technique could be used to test for radioactive byproducts from nuclear accidents or arms control treaty violations, for example, or for remote monitoring of smokestacks or factories for signs of air pollution or chemical weapons.

"You could imagine setting this up around the perimeter of an area where soldiers are living, as a kind of trip wire for nerve gas," said lead author Henry Everitt, an Army scientist and adjunct professor of physics at Duke University.

The technique uses a form of invisible light called terahertz radiation, or T-rays.

Already used to detect tumors and screen airport passengers, T-rays fall between microwaves and infrared radiation on the electromagnetic spectrum.

Zapping a gas molecule with a terahertz beam of just the right energy makes the molecule switch between alternate rotational states, producing a characteristic absorption spectrum "fingerprint," like the lines of a bar code.

Terahertz sensors have been used for decades to identify trace gases in the dry, low-pressure conditions of interstellar space or in controlled conditions in the lab, where they are capable of unambiguous identification and ultra-sensitive, part-per-trillion detection.

But until now, efforts to use the same technique to detect trace gases under normal atmospheric conditions have failed because the pressure and water vapor in the air smears and weakens the spectral fingerprint.

In a study published in the journal Physical Review Applied, Everitt, Ohio State University physicist Frank De Lucia and colleagues have developed a way around this problem.

Their approach works by blasting a cloud of gas with two beams at once. One is a steady terahertz beam, tuned to the specific rotational transition energy of the gas molecule they're looking for.

The second beam comes from a laser, operating in the infrared, which emits light in high-speed pulses.

At the U.S. Army Aviation and Missile Research, Development, and Engineering Center near Huntsville, Alabama, the researchers have installed a one-of-a-kind infrared laser.

Manufactured by a company called STI Optronics, it's capable of firing dozens of pulses of infrared light a second, each of which is less than a billionth-of-a-second long.

"It's kind of like whacking a molecule with an infrared sledgehammer," Everitt said.

Normal atmospheric pressure still blurs the chemical "bar code" produced by the blast of the Terahertz beam, but the ultra-short pulses of light from the more powerful infrared laser knock the molecule out of equilibrium, causing the smeared absorption lines to flicker.

"We just have to tune each beam to the wavelengths that match the type of molecule we're looking for, and if we see a change, we know it has to be that gas and nothing else," Everitt said.

The researchers directed the two beams onto samples of methyl fluoride, methyl chloride and methyl bromide gases in the lab to determine what combination of laser settings would be required to detect trace amounts of these gases under different weather conditions.

"Terahertz waves will only propagate so far before water vapor in the air absorbs them, which means the approach works a lot better on, say, a cold winter day than a hot summer day," Everitt said.

The researchers say they are able to detect trace gases from up to one kilometer away. But even under ideal weather conditions, the technology isn't ready to be deployed in the field just yet.

For one, converting an eight-foot, one-ton laser into something closer in size to a briefcase will take some time.

Having demonstrated that the technique can work, their next step is to figure out how to tune the beams to detect additional gases.

Initially, they plan to focus on toxic industrial chemicals such as ammonia, carbon disulfide, nitric acid and sulfuric acid.

Eventually, the researchers say their technique could also be useful for law enforcement in detecting toxic gases generated by meth labs, and other situations where detection at the gas's source isn't feasible.

"Point sensing at close range is always better than remote sensing if you can do it, but it's not always possible. These methods let us collect chemical intelligence that tells us what's going on before we get somewhere," Everitt said.

 Explore further: NIST 'combs' the atmosphere to measure greenhouse gases

More information: "Design and signature analysis of remote trace-gas identification methodology based on infrared-terahertz double-resonance spectroscopy," Tanner, E., et al. Physical Review Applied, 2014. dx.doi.org/10.1103/PhysRevApplied.2.054016

New Research In Ohio Labs Brings Star Trek Technology To Life

UC Davis researchers work on their project, "Terahertz Interconnect, the Last Centimeter Data Link"(Photo: Flickr Commons)

http://wosu.org/2012/news/2014/06/09/star-trek-technology-becoming-reality-in-ohio-laboratories/

Ohio is emerging as a global center of research in a branch of physics that’s stymied scientists for decades. It’s called Terahertz radiation, a band of light waves with potential uses that range from detecting cancer to uncovering art forgeries.

For those familiar with the original Star Trek series, they would remember the tricorder. Spock or McCoy could point the tricorder at anything, and instantly know its chemical makeup, see hidden objects, or diagnose diseases. A replica tricorder sits in the office of Teraphysics founder and president Jerry Mearini. As a fan of all things retro, and a physicist and entrepreneur, Mearini was inspired by the tricorder’s pretend powers.

“And when we started working on Terahertz devices, the first thing that came to my mind is we’re building the world’s first Star Trek Tricorder,” Mearini said.

He says it may not be science fiction much longer.

New technologies

“We’re not building the tricorder itself, we’re building the engine that drives it,” Mearini said.

The engine is a credit-card sized, high-power Terahertz generator— technology that’s eluded scientists since the 1960s.

Light is a spectrum. On one end you have high-energy, high-frequency X-rays; on the other end, low frequency radio waves – like the ones your car antenna captures. In the middle of the spectrum is visible light that you see all around you. People have made use of practically every part of that spectrum in one way or another, except for one. The Terahertz frequencies.

T-rays, as they’re called, fall between the heavily utilized wavelengths of infrared radiation—think night vision goggles and microwaves.

The Terahertz gap

But the equally promising Terahertz range has up until now been relatively inaccessible through existing technologies.  It’s been called the Terahertz gap.

“I wouldn’t describe it as a gap, but it is the spectral region that’s had the least attention, the fewest man years applied to it,” said Frank De Lucia, a physics professor at Ohio State. De Lucia is a pioneer in the field of Terahertz research. “And I think there’s a lot more virgin territory to explore and a lot more virgin things to find simply because it’s not been worked on much as a function of time.  And part of the reason for that is that it’s been difficult and expensive to build sources.”

And De Lucia says the practical, portable Terahertz source that Jerry Mearini has created is a significant jump forward.

Mearini said the tiny gold and diamond Terahertz generator is based on decades-old technology married to today’s nano-fabrication techniques. It’s about half the size of a human hair.

“It’s a vacuum tube, but a very modern day vacuum tube,” Mearini said. “But not unlike the glass vacuum tubes that are in my guitar amp at home, just a much cooler one.”

It took Mearini and his team 10 years of long nights to get it to work.

A new breakthrough

Teraphysics announced the breakthrough last month.

“It’s a paradigm shift because it would enable a whole class of new experiments that have not been conducted to date, or have not been conducted well to date, because of the lack of power in that frequency region,” said Elliott Brown, an expert in Terahertz technology at Wright State University in Dayton.

Brown sees enormous potential for the Teraphysics’ device, especially in biomedical imaging. In his lab, he uses T-rays to detect skin cancer, to diagnose burns, and to analyze DNA.

At Teraphysics in Cleveland, Mearini sees the potential of his device to identify chemicals, even at a distance.

“The most interesting aspect of Terahertz is that, in that frequency range, you can unambiguously identify molecular species, because most molecular species in that frequency range exhibit what we refer to as resonant signatures,” Mearini said.

Uses include public safety

The Terahertz spectrum can also ‘see’ through clothing and paper packaging.  It’s being tested in next generation airport scanners to detect hidden objects, or even the chemical signature of bomb material. T-rays are being used to link computer systems through high bandwidth wireless, also in secure communications, and data transfer. Other uses include inspection of paint and coatings, even uncovering art forgeries.

“It’s this unique area within the electro-magnetic spectrum that shows so much promise for so many applications that has really been tapped until now,” Mearini said.

The list of potential uses for Terahertz devices sounds like science fiction, but one Cleveland company, and researchers across Ohio, may soon make them a reality.