Research And Application On Photoacoustic Spectroscopy And Cavity Enhanced Absorption Spectroscopy Techniques

The quantitative determination of trace gas concentration is involved in the study of biological trace gas exchange, air pollution and medical diagnosis. The study of trace gas detection technology is expected to solve this problem. In this paper, the theory and application of photoacoustic spectroscopy and cavity enhanced absorption spectroscopy are studied in detail. The research works are outlined as follows:1. The theory of photoacoustic spectroscopy is described in detail, and is applied to the design of a low noise, high sensitivity longitudinal resonant acoustic cell. It is also used in designing the detection and data processing software. All of these are utilized to develop a high sensitivity photoacoustic spectrometer based on a COa laser, which could reach a detection limit of 10'11 for ethylene. Furthermore, we design a more compact photoacoustic spectrometer based on a waveguide COi laser.2. The above systems are used to measure the ethylene production of apples, nectarines and cherry -tomatoes. It is a good try of this technique in biological field.3. According to the theoretical analysis of the effect of dynamic cooling caused by energy exchange between COi and Na molecules, Levenberg-Marquardt algorithm for fitting nonlinear functions is applied to calculating the concentrations of multi-component gas mixture containing COa gas. Experiments have been carried out on measuring 03 and C2H4 concentration released from a Fuji apple and a motorbike exhaust respectively. The experimental results demonstrated the availability and validity of the nonlinear fit algorithm.4. The theory of cavity enhanced absorption spectroscopy is studied in detail and the numerical simulation is firstly demonstrated. In addition, we analyze the variation of sensitivity and linearity of this technique with the scan speed of incident light frequency or absorption cavity length.5. A Color Center Laser is firstly used to carry out cavity enhanced absorption spectroscopy. The triangular absorption cavity, which is firstly used in such an experiment, is scanned in the experiments and the absorption spectra of NaO are measured.6. An OPO resonant cavity is optimized to get a better lasing performance and the OPO isused to perform the cavity enhanced absorption spectroscopy detection of ethane.