Frontiers of molecular gas sensing

Mainly driven by the recent dramatic progress of infrared technologies, as well as by the emerging methods for cooling of ground-state molecules, the field of precision molecular spectroscopy is experiencing a new youth, as it promises to lead major advances both in fundamental and applied science. The present review will encompass the main results obtained in the last two decades, by our group, in this scope, particularly in the mid infrared and THz spectral regions. Starting from the development of novel, metrological-grade coherent radiation sources, either in continuous-wave or in pulsed-emission regime, we will go through the realization of more an more sophisticated spectroscopic interrogation techniques. We will then conclude with the first demonstration of cavity-enhanced ro-vibrational spectroscopy on a buffer-gas-cooled molecular beam. From this brief overview it emerges that high-precision physical fundamental measurements can be done, at present, at an energy scale as low as the photons used for harnessing the molecular samples.