Performance Optimization Study Of Optical-feedback Cavity Enhanced Absorption Spectroscopy

The cavity-enhanced absorption spectroscopy technology,which has the advantages of simple structure,high sensitivity and non-contact,has good application prospects in the fields of environmental gas detection,air pollution monitoring,molecular spectroscopy measurement and biomedical diagnosis.As a derivative technology of cavity decay spectroscopy,the cavity enhanced absorption spectroscopy has simpler system structure and more concise signal processing.Based on the above advantages,this technology is especially suitable for application in the field of medical nondestructive diagnosis and is expected to realize the clinical application of respiratory gas diagnosis technology.In this paper,we focus on improving the performance of the cavity-enhanced absorption spectroscopy system.In order to improve the detection performance of the system and promote its clinical application,several methods have been proposed based on our previous work in the field of optical feedback cavity-enhanced absorption spectroscopy technology.The specific work of this paper includes the following:（1）On the basis of summarizing the current situation of cavity-enhanced absorption spectrometry in the field of respiratory gas analysis at home and abroad in recent years,we analyzed the risks and challenges existed in the clinical application of respiratory gas,and proposed methods to improve the performance of the system;（2）Combing with the previous work of the group,we explored the expansion of the detection performance of the system based on the original V-cavity optical feedback cavity-enhanced absorption spectrometry system.Based on the original V-cavity optical feedback cavity-enhanced absorption spectroscopy system,we explore the expansion of the detection range of the system.After the minimum detectable absorption coefficient of 2.6858×10^-9 cm^-1 was measured,experimental measurements were performed for the selected CO absorption line near 1568.04 nm,and it was confirmed that the system could detect CO at the ppb level with an absorption intensity of 10^-23 cm^-1/(molecule·cm^-2).A new system of optical-electrical frequency-stabilized folded cavity enhanced absorption spectroscopy based on the combination of optical feedback and PDH frequency stabilization was designed and built.The anomalies and phenomena encountered during the system construction and experiments were analyzed,and improvement methods were proposed and experimentally verified.The experimental results show that the optical feedback cavity-enhanced absorption spectroscopy system with a combination of optical and electrical frequency stabilization can achieve a signal output with a stability better than0.34%.The minimum detectable absorption coefficient of the system is 7.6×10^-9 cm^-1obtained from the cavity enhanced absorption spectroscopy test of residual water vapor in the cavity.The measurement of ammonia absorption near the working wavelength using this system can achieve the concentration detection of ppb magnitude.The research work done in this paper is a useful exploration and practice to optimize the performance of the optical feedback cavity-enhanced absorption spectroscopy system.The work has important theoretical value and practical significance and will strongly promote the practical application of this technology in the clinical diagnosis of respiratory gases.