Cavity ring-down spectroscopy of Doppler-broadened absorption line with sub-MHz absolute frequency accuracy

C.-F Cheng,J Wang,S.-M Hu,Y Lu,Y R Sun,X.-F Li,A.-W Liu,H Pan

doi:10.1364/oe.20.009956

Abstract

A continuous-wave cavity ring-down spectrometer has been built for precise determination of absolute frequencies of Doppler-broadened absorption lines. Using a thermo-stabilized Fabry-Pérot interferometer and Rb frequency references at the 780 nm and 795 nm, 0.1 - 0.6 MHz absolute frequency accuracy has been achieved in the 775-800 nm region. A water absorption line at 12579 cm(-1) is studied to test the performance of the spectrometer. The line position at zero-pressure limit is determined with an uncertainty of 0.3 MHz (relative accuracy of 0.8 × 10(-9)).

Highlights

Precise transition frequencies of atoms and molecules are widely applied in science and technology, such as tests of fundamental symmetries and high-level ab initio calculations, standards used for laser frequency stabilization and spectral calibration
We have presented a different approach of FS-Cavity ring-down spectroscopy (CRDS) by locking the laser frequency to an external stabilized reference and scanning a sideband for spectroscopy through a radio-frequency driving electro-optic modulator [14]
Using a thermo-stabilized Fabry-Perot interferometer calibrated with atomic frequency references, sub-MHz absolute frequency accuracy has been achieved in the near infrared, which is less than one thousandth of the Doppler width of the line

Summary

Introduction

Precise transition frequencies of atoms and molecules are widely applied in science and technology, such as tests of fundamental symmetries and high-level ab initio calculations, standards used for laser frequency stabilization and spectral calibration. Cavity ring-down spectroscopy (CRDS) has been acknowledged as a very sensitive tool for absorption measurement for over 20 years. It has been widely applied in molecular spectroscopy and trace gas detection. An absorption loss of 10−10/cm or even less can be detected by a CRD spectrometer if the laser modes, both the spacial and the longitudinal, are matched to a high-finesse ring-down cavity [5,6,7,8,9]. Mode-matching of the spectral laser to the stabilized high-finesse ring-down cavity can lead to frequency resolution of about 1 MHz or better. Using a thermo-stabilized Fabry-Perot interferometer calibrated with atomic frequency references, sub-MHz absolute frequency accuracy has been achieved in the near infrared, which is less than one thousandth of the Doppler width of the line. A Dopplerbroadened ro-vibrational line of H126O is studied to test the performance of the spectrometer

Experimental

Performance test

Findings

Summary