Abstract
Cavity ringdown spectroscopy (CRDS) is a sensitive, accurate method to acquire weak optical absorption spectra. By measuring the ringdown time of light in a high finesse cavity filled with gas we can get the absorption coefficient of the gas. We use this method to measure the weak absorption spectrum of CO2 near 1064 nm.In this thesis, we use two methods to fit the experimental ringdown curve to obtain the ringdown time. The first method is fitting the experimental ringdown curve with the theoretical ringdown curve formula (RCF), and the reduced c2 we get is about 10-9. The second method is with the exponential decay formula (EDF), and the reduced c2 we get is about 10-8.The ringdown time obtained by the first method is about 15% larger than the second method. The reason for this difference is not clear now. Using the fitting results of RCF the absorption center of CO2 (2003←0000) R(6) transition we obtained is 9394.00513 cm-1 with an uncertainty of 2.4’10-4 cm-1.We also study the valid condition of the EDF fitting using the theoretical cavity ringdown curve as the experimental data. By neglecting the data before a "cut time", we can obtain the correct ringdown time using the EDF fitting.In the future, we will replace the reflective mirrors of the cavity to higher reflection ones to increase the finesse, and use the new cavity to measure the overtone spectrum of HD near 1 mm.