| Cavity Enhanced Absorption Spectroscopy(CEAS)is a new and highly sensitivity absorption spectroscopy developed from cavity ring-down spectroscopy.The technology has been widely applied in the qualitative and the quantitative detection of gaseous substances,including biomedicine,environmental monitoring,industrial detection and many other fields.CEAS has the advantages of simple system structure,fast measuring speed and so on.In recently years,It is a hot research topic in spectroscopy and has a very good application prospect in the field of medical nondestructive testing especially.In this paper,we study some ways in order to further improve the performance of Optical feedback cavity enhanced absorption spectroscopy(OF-CEAS)system and to solve some problems have been found during the research of OF-CEAS.The specific work of this paper includes:(1)Self-injection frequency-locking scheme is explored based on optical feedback technology.Theoretical model is established and some preliminary experiments are conducted.The experimental results are analyzed and discussed.(2)To further improve the performance of OF-CEAS system,the optical properties of the folded cavity is changed,including its loss and position distribution of three mirrors,the intensity of feedback signal and the loss of the folded cavity are optimized and reduced respectively.Experiments show that this method can improve the noise measurement sensitivity of OF-CEAS system and improve the detection accuracy of gas concentration to ppb level.(3)To improve the spectral responsivity(spectral range and response time)and the detection of gas species of the system,two different wavelengths of laser are periodically coupled into the folded cavity by switching optical path based on the principle of wavelength division multiplexing(WDM).The work done in this paper is of great significance to the application of OF-CEAS,and is expected to be applied in the human respiratory gas diagnosis. |
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