The Method And Some Applications Of Intra-cavity Laser Absorption Spectroscopy

The work included in this thesis is to record high-resolution overtone ro-vibrational spectra of small molecules in gas phase utilizing intra-cavity laser absorption spectroscopy (ICLAS) and the experimental improvement. In Chapter 1,ICLAS, a widely used spectral technique in recent years, is introduced. Emphases are put on the important issues such as principles of ICLAS, sensitivity, resolution and laser mode. From our experience, all these issues are of practical importance in our experimental work. In Chapter 2, the apparatus of ICLAS is introduced, the factors affected the quality of measured spectra are also discussed in detail. Utilizing the equipment in our lab, the performance of the Fourier-transform intra-cavity laser absorption spectroscopy ( FT-ICLAS) was tested by applying to the measurement of the weak bands of acetylene near 12300cm^-1 . The method to do absolute line intensities measurement was also demonstrated. Based on our previous setup, a signal differential module is introduced to reduce the noise rising from the fluctuation of the laser power to improve the quality of the experimental interferogram. In the third chapter, two examples were given to show the applications of FT-ICLAS. The fifth overtone of PH₃ near 12600cm^-1 was recorded, and the self-broadening and line shift parameters were obtained. A weak band of ¹³CO₂ near 8000cm^-1 was recorded to demonstrate the method to achieve sample temperature from the absorption line intensities. The possibility to get flame temperature from ICLAS spectrum is also discussed.