Dual-comb cavity-enhanced absorption and dispersion spectroscopy from cavity mode widths and mode shifts measurement

In the last decade dual comb spectroscopy (DCS) has matured into a powerful tool for applications in various fields [1] . However, combining DCS with an optical enhancement cavity is so far relatively unexplored, with only a few demonstrations until now [2] – [5] , which required the measurement of reference spectrum and the correction of the measured molecular spectrum for the comb-cavity frequency mismatch [6] . As a way to circumvent those limitations, we present dual-comb measurements of widths and positions of enhancement cavity modes to retrieve molecular absorption and dispersion spectrum and we demonstrate it on methane sample (20% mixture in nitrogen). This method has been previously demonstrated with continuous wave (CW) lasers [7] and broadband comb-based mechanical Fourier-transform (FT) [8] , and dispersive [9] spectrometers.