Abstract
Cavity ringdown spectroscopy (CRDS) is a sensitive,accurate way to acquire weak optical absorption spectra. Because there is a relation between absorption coefficient and ringdown rate in high finesse Fabry-Pèrot cavity, The absorption coefficient of a gas sample inside a is determined by the ringdown rate of the light inside the cavity.. We have set up a CRDS system to measure the weak absorption of CO2 (2003 ← 0000) R(6) transition in the tuning range of the 1064 nm Nd:YAG laser. The Fabry-Perot cavity is formed by a plane mirror and a spherical mirror of 1 meter radius of curvature with finesse about 5700. The cavity length is 62.9 cm. Using offset locking method, we can scan the spectrum by locking 100 mW Nd:YAG laser to a 500 mW Nd:YAG laser which stabilized to the absorption spectrum of I2, the accuracy of our experiment is 20 kHz. The absorption center in our experiment is 9394.005 ± 0.001 cm-1. The detection limit is about 5 × 10-8 cm-1. In the future, we will improve the detection sensitivity by one order of magnitude using mirrors with higher reflectivity. The CRDS system will be employed to detect the weak v = 0→3 overtone transitions of HD near 1000 nm.