  Mid-infrared dual-comb spectroscopy has the potential to supplant
conventional high-resolution Fourier transform spectroscopy in applications
that require high resolution, accuracy, signal-to-noise ratio, and speed. Until
now, dual-comb spectroscopy in the mid-infrared has been limited to narrow
optical bandwidths or to low signal-to-noise ratios. Using a combination of
digital signal processing and broadband frequency conversion in waveguides, we
demonstrate a mid-infrared dual-comb spectrometer that can measure comb-tooth
resolved spectra across an octave of bandwidth in the mid-infrared from 2.6-5.2
$\mu$m with sub-MHz frequency precision and accuracy and with a spectral
signal-to-noise ratio as high as 6500. As a demonstration, we measure the
highly structured, broadband cross-section of propane (C3H8) in the 2860-3020
cm-1 region, the complex phase/amplitude spectrum of carbonyl sulfide (COS) in
the 2000 to 2100 cm-1 region, and the complex spectra of methane, acetylene,
and ethane in the 2860-3400 cm-1 region.
