Absolute frequency measurement of sub-Doppler molecular lines using a 3.4-μm difference-frequency-generation spectrometer and a fiber-based frequency comb

Abstract

We measure the absolute frequency of 12 sub-Doppler lines of the P (6) and P (7) transitions in the ν3 band of C 12 H4 using difference-frequency- generation (DFG) of 1.064-μm Nd:YAG and 1.55-μm DFB lasers and a fiber-based frequency comb referenced to International Atomic Time. The relative uncertainties are typically 9.4× 10-11, and the determined value for the P (7) F2 (2) line agrees with the International Committee for Weights and Measures recommendation with a discrepancy of (1.2±8.4) kHz. The combination of the DFG spectrometer and the frequency comb enables determining energy levels as accurately as microwave spectroscopy. © 2009 The American Physical Society.