Metrology of methanol in the near-infrared at the 10^-13 level

This poster showcases the application of Noise-Immune Cavity-Enhanced Optical Heterodyne Molecular Spectroscopy (NICE-OHMS) for precision spectroscopy of methanol. This approach, invented almost thirty years ago 1 and further developed as an optical precision tool 2, allows the measurement as Lamb-dips of extremely weak transitions 3, combining both sensitivity and accuracy. We report sub-kHz precision measurements of three vibrational line pairs, corresponding to the 3−1E - 20E combination difference in the vibrationless ground state. This allows the determination of this 12.2 GHz radio line frequency, highly sensitive to potential variations in the proton-electron mass ratios 4, 5, at kHz precision. Furthermore, having moved our NICEOHMS setup, we present a comparison of results obtained in Amsterdam and Louvain-la-Neuve on these very accurate frequency determination of methanol resonances.