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Optimization of parabolic cell for gas Raman analysis

2019; Wiley; Volume: 50; Issue: 5 Linguagem: Inglês

10.1002/jrs.5564

1097-4555

Anlan Yu, Duluo Zuo, Xinbing Wang,

Spectroscopy and Laser Applications

Abstract Raman spectroscopy is a widely practicable technique in gas analysis, but the application in simultaneous detection of multiple‐trace gas is still a challenge for its weak signal level. To extend the application of Raman gas analysis to detection of trace gas constituents, a closed parabolic sample cell proposed in our previous work is optimized by optical analysis and experimental verification. The optical analysis shows that for a parabolic reflector with rim diameter 6 p ( p , semi‐latus rectum), the collecting solid angle can be as large as 90% of full space (4π) and the power‐collecting efficiency can be as high as 80%. The variation of the Raman signal level with the position of collecting aperture and the parameter p of parabolic reflector was verified by the experimental results. At the optimized structure parameters, we get a signal‐to‐background ratio of 122 and a signal‐to‐noise ratio of 305 in the Raman spectra of ambient air with exposure time of 1 s. From the results of standard analytic gaseous samples, the limits of detection of 33 ppm‐bar for H 2 , 38 ppm‐bar for CO, 19 ppm‐bar for CH 4 , 27 ppm‐bar for C 2 H 6 , 23 ppm‐bar for C 2 H 4 , and 20 ppm‐bar for C 2 H 2 were obtained with exposure time of 200 s. These results indicate that the parabolic sample cell is a competitive Raman collector, which showing good balance in signal enhancement and background level.