Gas detection & measurement
ACCELERATING PRECISION GAS SPECTROMETRY IN THE MWIR SPECTRUM
O
ne of the most effective tools in the fight against air pollution and carbon emissions is the technique of gas absorption spectrometry.
Used to detect gases such as carbon
monoxide (CO), carbon dioxide (CO2) and nitrogen oxide (NO), the technique is widely used in factories and processing plants, including semiconductor fabrication plants.
Gas absorption spectrometry takes advantage of the optical properties of gases in the Mid Wavelength Infra-Red (MWIR) wavelength band. Many gases of interest absorb light at a specific wavelength, with tuned lasers being a common light source – when compared
to a reference medium, a gas of interest will absorb some of the laser light, and the detected optical power of the source will be reduced.
The value of the absorption peak allows the accurate detection and identification of a specific gas. Based in Shanghai, MicroPhotons is a distributor of optical products as well as supporting its customers in the development of optical technology applications such as spectrometry and gas analysis and detection. The company was approached by a customer to help it with a project that called for accurate measurement of optical systems in the MWIR portion of the spectrum. The challenge for MicroPhotons was
that existing technologies for detecting gas absorption rates require the use of liquid nitrogen to cool the emitters. MicroPhotons planned to replace the super-cooled emitters with a super-continuum light source, allowing gas absorption measurements to be performed at room temperature.
Although more convenient and saving a large amount of test time, this approach requires very high measurement accuracy in the optical spectrum analyzer (OSA) used to characterise the light source. Also, the gases to be monitored had absorption peaks at wavelengths across the whole MWIR spectrum, from 1.9 to 5.5m - most OSAs are designed for use in telecoms systems, which only require measurement of wavelengths up to 1.7m. MicroPhotons was looking for a single instrument that could cover the entire MWIR spectrum. This could dramatically reduce test time and effort, avoiding the need to set up and calibrate more than one measurement instrument when testing equipment for the detection of gases with different absorption peaks. To meet its customer’s needs, MicroPhotons chose the AQ6377 OSA from Yokogawa. Across the 1.9 to 5.5m range, the AQ6377 is the only OSA capable of analysing the entire wavelength spectrum. The AQ6377 is the latest version
20 June 2024 Instrumentation Monthly
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