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Raman Signal Enhancement For Gas Detection Using A Near Concentric Cavity

Posted on:2014-04-30Degree:MasterType:Thesis
Country:ChinaCandidate:D W YangFull Text:PDF
GTID:2251330401485401Subject:Optical engineering
Abstract/Summary:PDF Full Text Request
Gas logging is an indispensable link in the oil-gas exploration. The speed and theprecision of the gas logging have effect on the veracity of oil-gas reservoir location, so itis the key point for improving the speed and precision of gas logging to developed a highspeed and precision gas detecting technology. The gas chromatographic method iswidely used in the gas logging, but because of the slow speed, complex equipment anddanger, it couldn’t meet the need of field application. The laser spectroscopy is a highspeed component analyzed method, the period of Raman spectrum and IR spectrum isabout dozens of seconds, and both of them have obvious signal about alkane, CO2andH2,but the constraint is the low sensitivity. The issue solved in this thesis is improvingthe sensitivity of Raman spectroscopy. This thesis had developed a method ofenhancing the intensity of Raman spectrum based on near-concentric cavity to solve thelow sensitivity of Raman spectrum. The whole work I had finished is the following:①The enhanced effect of the near-concentric cavity for the Raman spectrum had beanalyzed in this thesis. We expounded the relation between the intensity of the Ramanscatting and the scatting angle, studies show that the smaller the angle is the stronger theintensity of Raman spectrum is, so the intensity of the forward and the backward is thestrongest and the side is the weakest. Then we analyzed the enhanced effect of thenear-concentric cavity on that base. The aim of using the near concentric is enhancingthe intensity of the incident light and then the intensity of the Raman scatting is enhanced.Finally of this part we compare the enhanced effect the3multiple reflections modes, andthe result is that the near-concentric mode is the best one.②a system of Raman spectrum enhanced based on the near-concentric cavity wasbuilt in this part. In order to get a high intensity of spectrum we optimized someparameters of the setup. The Experimental results show that the angle between the collector and the laser beam is smaller, and the intensity of Raman spectrum is stronger;and the enhanced effect of the near-concentric line mode is the best among the3multiplereflections modes. Compared with the Raman spectrum without using the nearconcentric cavity, the spectrum of near concentric cavity is enhanced by about70times.③we have built up a back collection Raman spectrum gas detecting system toestimate the enhancement effect of the near concentric system. In this experiment, thevariable parameters are the same as the parameters of the near concentric system.Compare these two system from the intensity, the SBR and the SNR of the O2and N2signal, experimental result shows the Raman signal of the near concentric system is5times larger than the back collection system, and the limit of detection is about10timeslarger than the back collection system.Finally conclusion of this thesis and some insufficient analysis of this thesis havebeen given in the5thchapter, the prospect of future work was discussed in this part.
Keywords/Search Tags:Gas logging, methane, Raman signal enhancement, near concentric cavity, detection sensitivity
PDF Full Text Request
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