Near-Infrared Spectroscopy of Methanol at the 10−13 Level for Radio Astronomy

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 protonelectron mass ratios (4 5), at kHz precision. Furthermore, having moved our NICE-OHMS setup, we will be presenting a comparison of results obtained in Amsterdam and Louvain-la-Neuve on these very accurate frequency determinations of methanol resonances. 1. Ye, J., Ma, L.-S. and Hall, J.L. 1996, Optics Lett., 21, 13 2. Foltynowicz, A., Schmidt, F.M., Ma, W. and Axner, O. 2008, Appl. Phys. B, 92, 3 3. Cozijn, F.M.J., Diouf, M.L. and Ubachs, W. 2023, Phys. Rev. Lett, 131, 073001 4. Jansen, P., Xu, L.-H., Kleiner, I., et al. 2011, Phys. Rev. Lett, 106, 100801 5. Levshakov, S.A., Kozlov, M.G. and Reimers, D. 2011, ApJ, 738, 26