Molecules in optical resonators: Precision measurements and fundamental tests.

The advent of visible and near-infrared optical frequency combs, at the beginning of the century, gave a tremendous boost to precision laser spectroscopy. This technology enables absolute measurements of atomic and molecular transitions frequencies, thus taking a key role for fundamental tests and measurements. Recently, high-precision spectroscopic investigations have been extended to the weak absorption features of light molecules for testing first principles variational calculations that include relativistic and quantum electrodynamic (QED) effects. In this respect, the small transition strength can be compensated by the use of long-path techniques. I will describe some examples of successful combination of cavity-enhanced spectroscopic methods and optical frequency comb synthesizers, for the aims of quantitative spectroscopy of linear molecules. I will report on recent results obtained at Università degli Studi della Campania regarding line-center frequency metrology and high-quality line-intensity determinations, in comparison with the most refined quantum mechanical calculations.