Probing Buffer-Gas Cooled Molecules with Direct Frequency Comb Spectroscopy in the Mid-Infrared

We demonstrate cavity-enhanced direct frequency comb spectroscopy on buffer-gas cooled molecules. By coupling a mid-infrared frequency comb to a high-finesse cavity surrounding a 4 K buffer-gas chamber, we obtain rotationally resolved absorption spectra of multiple vibrational bands of nitromethane.