Optical Sensor for Unknown Gas Detection

Lawrence Livermore National Laboratory, Livermore, CA

Gas sensors are usually engineered to detect a specific molecule in one of many potential categories: toxic gases, combustible gases, and VOCs. A number of technologies, such as infrared, photoionization, catalytic, and electrochemical, are used to test for differing molecular species. Each method has specifications for resolution, sensitivity, temperature, and humidity range. Gas sensors are most useful when they have high sensitivity and flexibility in the gases they can detect.

An artist's cross section shows a sensor that uses infrared laser light to illuminate gases. Light is transmitted through a fiber-optic bundle into a hollow fiber waveguide, a small glass capillary with a highly reflective inner metal coating. The interaction of the gas with the laser light identifies the gas. (Image courtesy of Lawrence Livermore National Laboratory)

With that in mind, LLNL researchers have combined Raman and infrared (IR) spectroscopy methods in a single device. The sensor is able to detect, identify, and quantify a range of unknown gases. Raman spectroscopy records the degree of light scattered, while IR measures the amount of light that is absorbed. The combination of the two techniques results in complementary spectra that serve as molecular-level fingerprints of gaseous species. With fiber-based multi-pass cells, gas concentrations down to the parts-per-million, and even parts-per-billion, can successfully be detected and measured.

Among the advantages of this system, are that since it uses an optical sensor, it does not require electricity so it is safe for environments involving energetic materials. The combination of Raman and IR provides wide gas sensing capability

The double-pass IR probe reduces the length and size of the sensor, which allows miniaturization for portability and easy field deployment. It can be embedded in confined spaces for continuous monitoring, which leads to lower operating costs.

Its potential applications include continuous monitoring and detection of gases and gas mixtures, as well as identifying and quantification of unknown gas species

For more information, contact Lawrence Livermore National Laboratory at This email address is being protected from spambots. You need JavaScript enabled to view it..