An illustration showing how trace gases are detected in the field using a mobile dual-frequency comb laser spectrometer. Photo: Stephanie Sizemore and Ian Coddington/NIST

Dual-comb photothermal spectroscopy allows for rapid multi-gas detection

18 May 2022

Dr Ren Wei at the Department of Mechanical and Automation Engineering of the Chinese University of Hong Kong, and collaborators from Changchun Institute of Optics, Fine Mechanics and Physics have proposed a novel sensing technique, dual-comb photothermal spectroscopy, to drastically improve gas sensing technology.

Their findings, published in Nature Communications, could lead to wider applications in the detection of toxic gases to the measurement of chemical compounds in breath samples.

The new technique can detect several gas species at one time, including ammonia, carbon dioxide, carbon monoxide, hydrogen sulphide and hydrocarbons. The team successfully demonstrated a minimum detection limit of 8.7 parts-per-million of acetylene, a colourless and extremely flammable gas, in the hollow-core fibre with a total sample volume of only 0.17 microlitre, whereas conventional laser-based spectrometers require about 100,000 microlitres and a longer testing time to reach the same level of detection sensitivity.

The dual-comb photothermal spectroscopy method may also be used to produce more sensitive, precise, and rapid tests for human breath analysis.

“We are now actively looking at the development of novel COVID-19 tests and chemical analysers that can help address the current pandemic or future public health emergencies,” said Professor Ren. 

The image demonstrates the beating process that occurs in the hollow-core fibre when the dual-comb light (top left of the image) is transmitted through the gas-filled fibre. The optical interference induced between the two combs further causes the photothermal effect that modifies the refractive index of the sample gas.