Measurement Of Molecular Spectral Line Parameters Using Laser-locked Cavity Ring-down Spectroscopy

High sensitivity laser absorption spectroscopy is a powerful technique for molec-ular spectroscopy studies.It is widely applied in basic scientific researches and trace gas detection.High accuracy spectroscopic line parameters(e.g.line frequencies,line intensities,widths,and line profiles)which are essential in the quantitative analysis,are based on high-precision and high-sensitivity laboratory spectroscopy measurements.This thesis describes applications of laser-locked cavity ring-down spectroscopy(LL-CRDS)towards the determination of molecule spectroscopy parameters.Line frequen-cies with sub-MHz accuracy and line intensities with uncertainties better than 0.85%have been determined.The thesis is also devoted to develop portable CRDS setup for the trace gas detection.The main content of this thesis is as follows:The first chapter introduces the fundamental theory of molecular absorption spec-troscopy,the principles of several high-resolution spectroscopy techniques and CRDS.A simplified historical overview of laser-locked CRDS is also presented.The second chapter introduces the setup of laser-locked cavity ring-down spec-trometer and the experimental scheme,including the mechanical design of the ring-down cavity,the optical layout and the CRDS spectrum scanning method.The laser-locked cavity ring-down spectrometer reaches a detection limit as low as 4.8 ×10-12 cm-1.In order to compensate for dispersive effects in the refractive index of the absorp-tion gas,we have measured the dispersion spectrum by scanning the cavity modes.The performance of the spectrometer was evaluated by measuring the Doppler-broadened spectra of C02 around 6470.42 cm-1.Absolute transition frequency,which was refer-enced to an optical frequency comb,has been obtained with sub-MHz accuracy.Spec-tral parameters derived from both the absorption and dispersion spectra were also com-pared to those given in the spectral databases.The third chapter introduces new line intensity measurements of the(30011-00001)12C16O2 band with the laser-locked cavity ring-down spectrometer.Uncertainties of both computed and measured line intensities are at the level of sub-percentage.How-ever,there is a deviation,which is much larger than these claimed precision,among these computed results as well as the computed and measured results.For this reason,an independent high-accuracy line intensity measurement is needed.The line intensities were obtained with uncertainties better than 0.85%.Results from previous studies and new calculations are also compared to present measurements.The fourth chapter introduces the development of portable cavity ring-down spec-trometers.The cavity modes are used as a frequency reference.Based on the property of the ring-down cavity three prototype CRDS instruments have been constructed.The design,performance and the measurement of trace gases obtained with the instruments have been presented.