Frequency metrology of molecules in the near-infrared by NICE-OHMS.

T P Hua,S M Hu,J Wang,Y R Sun,A W Liu

doi:10.1364/oe.27.006106

Abstract

Noise-immune cavity enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) is extremely sensitive in detecting weak absorption. However, the use of NICE-OHMS for metrology study was also hindered by its sensitivity to influence from various experimental conditions such as the residual amplitude modulation. Here we demonstrate to use NICE-OHMS for precision measurements of Lamb-dip spectra of molecules. After a dedicated investigation of the systematic uncertainties in the NICE-OHMS measurement, the transition frequency of a ro-vibrational line of C2H2 near 789 nm was determined to be 379 639 280 915.3±1.2 kHz (fractional uncertainty 3.2 × 10-12), agreeing well with, but more accurate than, the value determined from previous cavity ring-down spectroscopy measurements. The study indicates the possibility to implement the very sensitive NICE-OHMS method for frequency metrology of molecules, or a molecular clock, in the near-infrared.

Highlights

Precise frequency measurements of molecular transitions play an essential role in widespread applications, such as frequency metrology [1], astronomy [2,3], and molecular spectroscopy [4,5]
The noise immune cavity enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) technique combines the advantage of frequency modulation for reduction of noise and that of the cavity enhancement of the absorption path
We report a comparison between NICE-OHMS and Cavity ring-down spectroscopy (CRDS) in metrology study of molecules, by measuring the Doppler-free saturated absorption spectrum of an acetylene line near 789 nm which has been recently measured by CRDS [34]

Summary

Introduction

Precise frequency measurements of molecular transitions play an essential role in widespread applications, such as frequency metrology [1], astronomy [2,3], and molecular spectroscopy [4,5]. The sensitivity of detection can be considerably improved by using cavity enhancement absorption spectroscopy (CEAS) [19, 20], which takes advantage of a high finesses optical cavity to increase the optical path length. The noise immune cavity enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) technique combines the advantage of frequency modulation for reduction of noise and that of the cavity enhancement of the absorption path. The high-finesse optical resonant cavity enhances the effective absorption path length, and significantly enhances the light power in the cavity It allows saturation spectroscopy using low-power continuous-wave lasers [31]. We report a comparison between NICE-OHMS and CRDS in metrology study of molecules, by measuring the Doppler-free saturated absorption spectrum of an acetylene line near 789 nm which has been recently measured by CRDS [34]. We implemented an optical reference with a stability of 3 × 10−13 by locking a laser at the molecular line center using NICE-OHMS

Experimental

Results and discussion

Conclusion