Low-cost resonant cavity Raman gas probe for multi-gas detection

Abstract

Raman based gas sensing can be attractive in several industrial applications, due to its multi-gas sensing capabilities and its ability to detect O 2 and N 2 . In this article, we have built a Raman gas probe, based on low-cost components, which has shown an estimated detection limit of 0.5 % for 30 second measurements of N 2 and O 2 . While this detection limit is higher than that of commercially available equipment, our estimated component cost is approximately one tenth of the price of commercially available equipment. The use of a resonant Fabry-Pérot cavity increases the scattered signal, and hence the sensitivity, by a factor of 50. The cavity is kept in resonance using a piezo-actuated mirror and a photodiode in a feedback loop. The system described in this article was made with minimum-cost components to demonstrate the low-cost principle. However, it is possible to decrease the detection limit using a higher-powered (but still low-cost) laser and improving the collection optics. By applying these improvements, the detection limit and estimated measurement precision will be sufficient for e.g. the monitoring of input gases in combustion processes, such as e.g. (bio-)gas power plants. In these processes, knowledge about gas compositions with 0.1 % (absolute) precision can help regulate and optimize process conditions. The system has the potential to provide a low-cost, industrial Raman sensor that is optimized for specific gas-detection applications.

Gas-phase Raman spectroscopy of non-reacting flows: comparison between free-space and cavity-based spontaneous Raman emission

“…Such feedback loops may either adjust the optical frequency of the laser to match the cavity frequency, or adjust the cavity length via a piezoelectric actuator. A number of different techniques have been used for locking the cavity into a resonance state [30,[56][57][58].…”

“…However, a number of different approaches have been proposed to enhance the signal such as confining light in a fiber (Fiber Enhanced Raman Spectroscopy (FERS)) or amplifying the signal by using a resonant mirrored cavity. Cavity Enhanced Raman Spectroscopy (CERS) uses the ability of mirrored cavities to enhance the input power, by tuning the cavity to particular modes of the input laser wavelength [29,30]. The approach takes advantage of the availability of affordable mirrors with high reflectivity surfaces, controllable mirror support bases, and inexpensive detection capabilities using low cost detectors or arrays.…”

“…al. [30] constructed a low-cost CERS probe for multi-gas detection. A 532 nm laser pointer was coupled into a Fabry-Perot cavity which allowed an increase in the sensitivity of the gas probe by a factor of 50.…”

Raman Gas Analyzer (RGA): Natural Gas Measurements

“…1,2 Raman gas analysis, because of low intensity of informative signals caused by small scattering cross-sections and low density of molecules in the gas phase, is less developed. However, interest in this direction of research has recently increased [3][4][5][6] due to the active development of hollow-core fibers, [7][8][9][10][11][12] appearance of high-power small-sized lasers and high-sensitive multichannel photodetectors. 13,14 In addition, it should be noted that nowadays first commercial Raman gas analyzers 15 start to appear, and despite the fact that their sensitivity is relatively low (0.01%) so far, there is a great potential for the development of this direction.…”

Quantitative Detection of Ethanol/Acetone in Complex Solutions Using Raman Spectroscopy Based on Headspace Gas Analysis

“…11 With the active development of surface-enhanced Raman scattering (SERS) and the appearance of hollow-core fibers, high-power small-sized lasers, and high-sensitivity multichannel photodetectors, more gas-sensing studies have emerged. [14][15][16][17] In 2014, Hanf et al reported a fiber-enhanced Raman spectroscopy system for multigas analysis. 18 In 2015, Deng et al proposed a headspace thin-film microextraction technique that was coupled with SERS to detect sulfur dioxide in wine.…”