Abstract：The detection of dissolved gases in seawater plays an important role in ocean observation and exploration. Raman spectroscopy has a great advantage in simultaneous multiple species detection and is thus regarded as a favorable choice for ocean application. However, its sensitivity remains insufficient, and a demand in enhancements is called!for before putting Raman spectroscopy to actual usein marine studies In this work, we developed a near-concentric cavity, in which laser beam could be trapped and reflected back and forth, for the purpose of intensifying Raman signals. The factors that would influence Raman signalswere taken into account. The result show that the smaller angle between collection direction and optical axis of reflection mirror, the stronger the signal and signal to noise ratio (SNR) is. With a collection angle of 30°, our Near-concentric Cavity System managed to raise the SNR to a figure about 16 times larger than that of common methods applying 90°. Moreover, the alignment pattern in our system made it possible to excel concentric cavity with a 3 times larger SNR. Compared with the single-pass Raman signal, the signal intensity ofour near-concentric cavity was up to 70 times enhanced. According to the obtained results of CO2 measurement, it can be seen that the new system providesa limit of detection(LOD) for CO2 about 0.19 mg·L-1 using 3-σ criterion standard, and the LOD of 11.5 μg·L-1 for CH4 was evaluated with the theoretical cross section values of CO2 and CH4.
Key words：Raman signal enhancement;Near concentric cavity;Detection sensitivity;Methane
杨德旺，郭金家，杜增丰，王振南，郑荣儿* . 近共心腔气体拉曼光谱增强方法研究 [J]. 光谱学与光谱分析, 2015, 35(03): 645-648.
YANG De-wang, GUO Jin-jia, DU Zeng-feng, WANG Zhen-nan, ZHENG Rong-er* . Raman Signal Enhancement for Gas Detection Using a Near Concentric Cavity . SPECTROSCOPY AND SPECTRAL ANALYSIS, 2015, 35(03): 645-648.
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