Mid-infrared dual-comb spectroscopy with electro-optic modulators
  We demonstrate dual-comb spectroscopy based on difference frequency generation of frequency-agile near-infrared frequency combs, produced with the help of electro-optic modulators. The combs have a remarkably flat intensity distribution and their positions and line spacings can be selected freely by simply dialing a knob. We record, in the 3-micron region, Doppler-limited absorption spectra with resolved comb lines within milliseconds. Precise molecular line parameters are retrieved. Our technique holds promise for fast and sensitive time-resolved studies e.g. of trace gases. 
Ming Yan, Pei-Ling Luo, Kana Iwakuni, Guy Millot, Theodor W. H\"ansch   and Nathalie Picqu\'e
physics.optics physics.chem-ph