| Precision spectroscopy reveals subtle atomic and molecular structures and plays an important role in modern physics and chemistry.High-precision measurements of molecular absorption line intensities can realize quantitative analysis of trace molecules.High-precision measurements of molecular transition frequencies can be used as a fre-quency reference,test the physics laws,and even explore new physics beyond the Stan-dard Model.The mid-infrared region(400-4000 cm-1),which contains strong funda-mental ro-vibrational transitions of many molecules,is of great interest in molecular spectroscopy.However,the frequency accuracy in this region is often limited by the lack of a narrow-linewidth tunable coherent light source.This dissertation focuses on building a tunable narrow-linewidth optical parametric oscillation light source system with a high frequency accuracy and its application in sensitive cavity ring-down spec-troscopy technique for high-precision molecular spectroscopy study.The main contents of this dissertation are organized as follows:The 1st chapter briefly introduces the importance of high-precision molecular spec-troscopy in terms of the intensity and frequency of molecular transitions.The saturated absorption spectroscopy,which is often used in high-precision transition frequency measurement,is also presented.The 2nd chapter introduces the optical parametric oscillator used as the mid-infrared light source in this work,detailed from the principle and setups.The method of precise frequency calibration of the optical parametric oscillator using an optical fre-quency comb is also presented.The 3rd chapter introduces the seeded narrow-linewidth optical parametric oscilla-tor system.The system’s precision measurement capability was demonstrated by mea-suring Lamb-dips of two transitions of methane and ethylene molecules.Experiments show that the frequency accuracy of the measurement is at the kHz level.The 4th chapter introduces the comb-locked narrow-linewidth optical parametric oscillator combined with a cavity ring-down spectroscopy device.The Doppler shift effect of cavity length modulation is also investigated.Lamb-dips of two nitrous oxide transitions around 2.7 microns have been measured with the system,exhibiting kHz accuracy.The 5th chapter summarizes this work and proposes further improvements for the experimental device,the OPO-based frequency-locked cavity ring-down spectroscopy.Moreover,the prospects of some important research goals that could be conducted with this system have also been presented... |
