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The Future of Gas Detection Meets Innovations in Absorption Spectrometry

by Yokogawa Test&Measurement March 18, 2024

With the world increasingly focused on environmental issues, we are all becoming more aware of carbon dioxide emissions and how to prevent them. As well as this, there are industrial gases from many chemical and production processes that cause pollution and need to be controlled.

As they say, if you can’t measure it, you can’t control it and keeping track of gases relies on highly accurate techniques that quicky identify the composition of a gas stream.

One 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 nitrous oxide (NO), the technique is widely used in factories and processing plants, including semiconductor fabrication facilities.

An optical technique, gas absorption spectrometry uses the fact that many gases of interest absorb light at a specific wavelength – shine a laser through them and they will absorb some of the laser light. A detector set to measure the light will show a decrease in the laser’s power characteristic absorption, helping identify the specific gas.

Optical measurement solutions are the specialty of Shanghai based MicroPhotons, a distributor of optical products as well as a system integrator that helps customers develop optical technology applications. A customer turned to the company when it needed accurate measurement of optical systems in the Mid Wavelength Infra-Red (MWIR) portion of the spectrum.

High accuracy essential

In a conventional set up, liquid nitrogen would be used to cool the emitters. This is a tricky technique, requiring large amounts of testing time. To get around this, MicroPhotons planned to replace the super-cooled emitters with a super-continuum light source.

The challenge for MicroPhotons was that this approach requires an optical spectrum analyzer (OSA) with very high measurement accuracy in order to characterize the light source.

Also, the gases to be monitored had absorption peaks at wavelengths across the whole MWIR spectrum, from 1.9μm to 5.5μm – getting a suitable instrument could be difficult, as most OSAs are designed for use in telecoms systems, which only need measurements up to 2μm.

To meet its customer’s needs, MicroPhotons chose the AQ6377 OSA from Yokogawa. Across the 1.9μm to 5.5μm range, the AQ6377 is the only OSA capable of analyzing the entire wavelength spectrum. Using a single instrument for all the measured wavelengths would cut test time and effort, avoiding the need to set up and calibrate more than one measurement instrument for different gasses.

Outstanding results

The AQ6377 achieves wavelength measurement accuracy of ±0.5nm and provides a close-in dynamic range of 50dB – this means that signals in close proximity can be clearly separated and accurately measured.

To prove the instrument’s accuracy, MicroPhotons ran measurements of the absorption of emissions from the characterized super-continuum light source.

The measurement results very closely tracked the data provided by the SpectraPlot online tool, a reference for the optical characteristics of gases. This gave MicroPhotons great confidence that the measurement output from the AQ6377, which it used to characterize the light source, is extremely accurate and repeatable over its very broad measurement bandwidth.

Detecting gasses accurately is increasingly important – with the Yokogawa AQ6377, developers and users of gas spectrometry can be sure they have the right instrument to accurately characterise the light source that lies at the heart of this essential technology.

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