Comb-calibrated Stimulated-Raman Spectroscopy of H2

One of the most intriguing molecular targets for testing quantum electrodynamics and physics beyond the standard model is H 2 , the simplest neutral molecule in the Universe and the recent subject of intensive theoretical and experimental studies [1]. Most rovibrational measurements on H 2 have been performed so far i) on overtone transitions to benefit for the strong signal enhancement given by high-finesse optical cavities in the near-infrared, ii) at relatively high pressures (0.01-1 atm) to compensate for the inherent weakness of quadrupole transitions, iii) recurring to models well beyond the Voigt profile to accurately fit spectra and eventually extrapolate transition frequencies to zero pressure. With the goal to target fundamental rovibrational transitions and in a future purely rotational lines, possibly at lower pressures, we have set out to develop an accurate nonlinear spectroscopy setup combining Stimulated Raman Scattering (SRS) with an optical frequency comb to calibrate the frequency axis.