Abstract

We present a thorough analysis of the signal line shapes of Fourier-transform-based noise-immune cavity-enhanced optical frequency comb spectroscopy (NICE-OFCS). We discuss the signal dependence on the ratio of the modulation frequency, $f_m$, to the molecular linewidth, $\mathrm{\Gamma }$. We compare a full model of the signals and a simplified absorption-like analytical model that has high accuracy for low $f_m/\mathrm{\Gamma }$ ratios and is much faster to compute. We verify the theory experimentally by measuring and fitting the NICE-OFCS spectra of ${\mathrm{CO}}_2$ at 1575 nm using a system based on an Er:fiber femtosecond laser and a cavity with a finesse of $\sim 11000$.

© 2017 Optical Society of America

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