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Research On Near-infrared Co2 Precision Molecular Spectroscopy

Posted on:2021-04-27Degree:MasterType:Thesis
Country:ChinaCandidate:X ZhangFull Text:PDF
GTID:2381330629487198Subject:Electrical engineering
Abstract/Summary:PDF Full Text Request
As the first greenhouse gas produced by human activities,carbon dioxide has become a key factor for global warming and the greenhouse effect.Its spectral parameters are important for monitoring global carbon dioxide concentration and distribution,limiting carbon emissions,and ensuring fair carbon trading.However,there are some disadvantage in the currently used spectroscopic measurement methods,and it is difficult to accurately obtain spectral parameters such as broadening and narrowing of the carbon dioxide transition line.In this paper,based on Cavity Ring-down Spectroscopy(CRDS),with the molecular vibration absorption spectrum and thermodynamic theory,the CRDS system is studied and analyzed,and a high-precision locked ring-down device and measurement method are proposed.The experiment measured five transition lines of carbon dioxide around 1.6 microns and obtained carbon dioxide precise molecular spectral parameters.Specifically,the research content of this paper mainly includes the following five aspects:1.Starting from the molecular energy level,the principle of absorption of photons of specific frequencies by molecules is analyzed,and the loss of the ringing cavity is related to the lifetime of the photon in the cavity.2.An optical ringing device with adjustable cavity length is proposed.Through the analysis of the optical cavity ring-down system and the analysis of the cavity length locking principle,a transmission model of the ring-down cavity is constructed.By designing the optical path system and the circuit system,a high-precision locking ring device measurement system is established.3.Build a locking ringing device system based on electro-optic modulator.The frequency-stabilized He-Ne laser is used as the reference light source,and the positive side-band modulated by the electro-optic modulator to the laser is used as the reference frequency.A driving signal is generated by the function generator to act on the piezoelectric ceramic to quickly change the cavity of the decaying cavity.After the long term comparison,analyze,the signal captured by the detector with thereference frequency signal will be used to extract the error signal,use the PID servo controller to initially lock the ringing cavity,change the modulation depth and PID controller gain and other related parameters to optimize the locking effect so the uncertainty of the locking error of the cavity is close to the uncertainty level of the reference laser.4.Analyze the optical cavity ring-down spectrum device system based on frequency stabilization.For the optical cavity ring-down spectroscopy system based on frequency stabilization,it is mainly divided into two parts: one is the cavity length locking system;the other is the trace gas measurement system.At the same time,the gas circuit system is briefly explained,and the measurement method of the whole system in actual work is given.5.Five transition lines of carbon dioxide around 1.6 microns were measured.Firstly,the selection of the measured spectrum lines is explained,the currently used molecular spectral line types are analyzed,and the spectral fitting software is used to perform single and multi-spectral fitting on the experimental data of the five spectral lines,and the fitting results are compared with the existing database parameters.Comparing and verifying the reliability of the experimental data,and finally analyzing the sources of errors in the experiment.
Keywords/Search Tags:Carbon dioxide, Optical cavity Ring-down, Mode matching, Absorption spectrum, molecular line-shape, Spectrum fitting
PDF Full Text Request
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