High-precision laser spectroscopy of the CO A$^1\Pi$ - X$^1\Sigma^+$ (2,0), (3,0) and (4,0) bands

TL;DR

This study achieved high-precision measurements of CO molecular transition frequencies using advanced laser spectroscopy techniques, providing data crucial for astrophysical tests of fundamental constant variations over cosmic time.

Contribution

The paper reports the first high-precision, Doppler-free frequency measurements of specific CO transitions with unprecedented accuracy, employing innovative experimental methods.

Findings

Absolute frequencies determined with 1.6×10⁻³ cm⁻¹ accuracy

Measured transition frequencies enable precise astrophysical comparisons

Laboratory wavelength accuracy supports tests of fundamental constant stability

Abstract

High-precision two-photon Doppler-free frequency measurements have been performed on the CO A$^1\Pi$ - X$^1\Sigma^+$ fourth-positive system (2,0), (3,0), and (4,0) bands. Absolute frequencies of forty-three transitions, for rotational quantum numbers up to $J = 5$, have been determined at an accuracy of $1.6\times10^{-3}$ cm$^{-1}$, using advanced techniques of two-color 2+1' resonance-enhanced multi-photon ionization, Sagnac interferometry, frequency-chirp analysis on the laser pulses, and correction for AC-Stark shifts. The accurate transition frequencies of the CO A$^1\Pi$ - X$^1\Sigma^+$ system are of relevance for comparison with astronomical data in the search for possible drifts of fundamental constants in the early universe. The present accuracies in laboratory wavelengths of $\Delta\lambda/\lambda = 2 \times 10^{-8}$ may be considered exact for the purpose of such comparisons.