Trace Gas Detection Based On Tube-cantilever Double Resonance Enhanced Photoacoustic Spectroscopy

Along with the rapid economic development,industrialization and urbanization construction acceleration,the problem of environmental pollution has become increasingly prominent.At the same time,the application of characteristic gas analysis of faulty electrical equipment,coal mine safety production monitoring and medical exhalation diagnosis also have an increasing demand for trace gas detection.Ultra-high sensitivity detection of target gas is helpful for accurate analysis and early warning.Therefore,the research of high sensitivity trace gas detection technology has important scientific significance and social application prospect.The main work of this paper is summarized as follows:In this paper,a new all-optical PAS trace gas detection technology based on the fiber optical cantilever acoustic sensor is proposed: a narrow linewidth distributed feedback(DFB)laser is used as the photoacoustic excitation light source,the dual resonance enhancement mechanism of the cantilever and resonator is introduced,and a new enhanced all-optical fiber FPI acoustic detection technology based on high-speed spectral demodulation is constructed to a new enhanced CEPAS.Through theoretical and finite element analysis,the design parameters of the cantilever beam are optimized,and a high sensitivity optical fiber cantilever microphone is designed.The double resonance was achieved at a frequency of 1408 Hz with a sensitivity of 2223.8 nm/Pa.By adjusting the parameters of the cantilever,the resonance frequency of the cantilever and the resonance tube is basically equal.The resonant frequency of the resonant tube is sensitive to temperature,and then the resonant frequency of the cantilever and the resonant tube can be precisely matched by adjusting the temperature of the photoacoustic cell.The test results of acetylene gas show that the feasibility of the system is verified by the experiments of different concentrations of acetylene gas.The experimental results show that the designed double resonance PAS system has an ultra-high response of3144 pm / ppm and a good linear response to different acetylene concentrations in the range of 0-100 ppm.The normalized equivalent noise coefficient(NNEA)of double resonance enhanced PAS system is 4.2 × 10-10cm-1 ·W· Hz-1/2.In addition,the minimum detection limit(MDL)of the system is 27 ppt with a 200-s averaging time by Allan-Werle deviation analysis.In this paper,the photoacoustic excitation unit and sensing unit is realized in optical fiber,which not only makes the system having the ability of electromagnetic immunity and intrinsicsafety,but also provides a reference for remote telemetry and multi-point measurement.The research of this paper will provide theoretical and experimental basis for the development of new ultra-high sensitivity all optical photoacoustic spectroscopy.