Electronic components speed spectroscopy

Ashley N. Rice, ashley.rice@photonics.com

Using electronic components could make atmospheric-gas measurement more even and 1000 times faster than with conventional techniques, and could advance greenhouse-gas measurement. Spectroscopy is the most common method for detecting trace gases. Until now, tuning a laser to shine in a wide enough range of colors typically required a mechanical device to change the frequency, but all of the methods available adjust the laser too slowly to obtain meaningful snapshots of the turbulent atmosphere.

An artist’s conception compares current spectroscopic gas-measurement technology with the NIST team’s improvement, which changes the scanning laser’s frequency evenly and more than 1000 times faster, permitting full-spectrum scans within a few milliseconds.

Now, scientists at the National Institute of Standards and Technology (NIST) have overcome an issue preventing the effective use of lasers to rapidly scan samples. They combined an electro-optic modulator and an optical resonator to alter the laser so that its light shines in a number of frequencies, then filters the frequencies so that the laser shines in only one color at any given instant.

The method permits a full spectrum of frequencies to pass through a gas sample in a few milliseconds or less, providing a clearer and more accurate resulting spectrum than previous “slow scan” methods.

“One of the major goals in climate science is to combine a wide variety of high-accuracy atmospheric measurements – including ground-based, aircraft and satellite missions – in order to fully understand the carbon cycle,” said David Long, a scientist in NIST’s Chemical Sciences Div. “The technology we’ve developed is general enough to be applicable for each of these platforms. The high speed of the technique allows for very accurate measurements of atmospheric gases at rates which are faster than atmospheric changes in temperature and pressure due to turbulence.”

The technique was demonstrated in a controlled laboratory environment using a small sample chamber for ground-based measurements, but the researchers say that if the scanner is mounted on a vehicle, an aircraft or a satellite, it also could work at great distances.

Applications for the technique include searching for hidden explosives and monitoring chemical processes in industry and the environment, the investigators say. They have applied for a patent.

The findings were reported in Nature Photonics (doi: 10.1038/nphoton.2013.98).