High-speed spectroscopy aids greenhouse gas detection

The team claims the technique also could work for other jobs that require gas detection, including the search for hidden explosives and monitoring chemical processes in industry and the environment.

Searching for faint whiffs of an unusual gas mixed in the air is called “trace gas sensing” and by far, the most common method is spectroscopy.

Accurately measuring the concentrations of relatively low-concentration gases, however, requires a lot of light, generated by a laser that can be tuned to different colours.

Until now, tuning a laser to shine in a wide enough range of colours typically has required a mechanical device to change the frequency.

The high speed of the technique allows for very accurate measurements of atmospheric gases

However, all the available methods adjust the laser too slowly to obtain meaningful snapshots of the turbulent atmosphere.

“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 the research team’s David Long, a scientist in NIST’s Chemical Sciences Division.

“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 team found a solution using electronics that permit fast and discrete changes in frequency. The components – called an electro-optic modulator and an optical resonator – work together to alter the laser so that its light shines in a number of different frequencies, and then to filter these frequencies so that the laser only shines in one color at any given instant.

The new method allows a wide range of different frequencies to pass through a gas sample in a few milliseconds or less, with the added benefit of providing a clearer and more accurate resulting spectrum than the previous “slow scan” methods could.

The team have published a research paper which details the use of the technique in a controlled laboratory environment using a small sample chamber for ground-based measurements.

Long said the group has submitted other papers with data indicating the technique also could work at great distances – potentially allowing a scanner to be mounted on a vehicle, an aircraft or a satellite.

The team also has applied for a patent on its work.