Description
Ultralight bosonic dark matter may induce oscillations of fundamental constants such as the fine-structure constant α and the proton-to-electron mass ratio μ, which can be searched for through precision spectroscopy. We present a molecular spectroscopy platform developed to search for such signals using the REFIMEVE optical frequency dissemination network. An ultrastable optical reference at 1542 nm, disseminated from the Paris Observatory to the University of Lille through an actively noise-compensated fiber link, is directly used as the frequency reference for the experiment.
The setup combines optical amplification, single-sideband frequency synthesis and active intensity stabilization to probe the P(27) transition of the v₁+v₃ band of ¹²C₂H₂ near 1542 nm. Differential balanced photodetection provides efficient suppression of common-mode intensity noise and enables high-sensitivity monitoring of the molecular absorption. The transition was characterized with an experimental linewidth of 768(33) MHz. The detector signal was further converted into an equivalent fractional frequency-noise spectrum over a bandwidth extending to the GHz range, providing a quantitative assessment of the sensitivity to oscillating variations of α and μ.
Although the present sensitivity does not yet reach that of the most competitive atomic-clock searches, these results demonstrate the feasibility of molecular dark-matter searches directly referenced to a distributed ultrastable optical network. The approach provides a scalable basis for future multi-site, correlated measurements using the REFIMEVE infrastructure.