'Ghost imaging' could make greenhouse gas analysis more precise

According to a new study, a novel imaging technique, called "ghost imaging," could help scientists more precisely measure atmospheric greenhouse gases.

"Monitoring atmospheric greenhouse gases such as methane, carbon dioxide, nitrous oxide and ozone is important for assessing how changing levels of these gases relates to climate change," Caroline Amiot, researcher at the Tampere University of Technology in Finland, said in a news release. "In some specific circumstances, our method could enable more sensitive detection of greenhouse gases, providing more accurate information about these important chemical compounds."

Ghost imaging works by integrating the signals of two individual light beams, which on their own may not offer insights into the nature of the sample object through which the wavelengths passed.

The process of measuring a gas molecule's effect on a light beam's spectral properties is called spectrography. Because gas molecules are usually relatively far apart, spectral analysis requires either an extremely bright light source or especially sensitive detector.

"Because our technique works by detecting an integrated signal containing many wavelengths -- as opposed to one wavelength like traditional spectroscopy methods -- it enables measurements using less powerful light sources and at wavelengths where highly sensitive detectors aren't available," Amiot said.

The new technique uses an initial light pulse to probe the gas sample, then a second that is compared to the first. Each pulse features a supercontinuum light beam with many wavelengths of light. The spectral fluctuations measured with the probing pulse provide context for the second spectral signature.

Scientists think the integrative approach -- described this week in the journal Optics Letters -- will avoid some of the distortion problems associated with typical greenhouse gas measurement techniques, which typically use high-power laser light.

"In order to measure which gas is present and at what quantity, the very faint light signal that comes back must be further split into various wavelengths for detection," said Amiot. "This may be problematic when the signal is very weak. Our method detects all the wavelengths mixed together, creating a much stronger signal that allows more sensitive measurements."

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