Mid-IR frequency control using an optical frequency comb and a remote near-infrared frequency reference

Ultra-high-resolution spectroscopy enables to test modern theories of fundamental physics with molecules as for instance the non conservation of parity [1] or the stability of the electron-to-proton mass ratio [2]. However many of these tests rely on the availability of ultra-stable and accurate laser sources emitting in the mid-infrared (MIR) where molecules exhibit rovibrational transitions. It is thus very challenging to develop a frequency stabilization scheme in the MIR which does not depend on quite rare secondary frequency references.