Fig. 4.
Three different categories of DCS demonstrations. (a) Free-running combs can yield dual-comb spectra, but with low resolution, low frequency accuracy, and low SNR, since only limited signal averaging is possible; (b) mutually coherent combs can yield comb-tooth-resolved spectra that can be averaged for high SNR; and (c) fully referenced combs yield spectra with simultaneous high resolution, absolute frequency accuracy, and high SNR. Text boxes indicate some general rules of thumb for frequency combs based on mode-locked lasers.