Octave-spanning dual frequency comb spectroscopy in the molecular fingerprint region
Henry R. Timmers, Abijith S. Kowligy, Alexander J. Lind, Flavio Caldas da Cruz, Nima Nader, Myles C. Silfies, Thomas K. Allison, Gabriel G. Ycas, Peter G. Schunemann, Scott B. Papp, Scott A. Diddams
Spectroscopy in the molecular fingerprint spectral region (6.5-20 $\mu$m) yields critical information on material structure for physical, chemical and biological sciences. Despite decades of effort, this portion of the electromagnetic spectrum remains challenging to cover with conventional laser technologies. In this report, we present a simple and robust method for generating super-octave, optical frequency combs in the fingerprint region through intra-pulse difference frequency generation in an orientation-patterned gallium phosphide crystal. We demonstrate the utility of this unique coherent light source for high-precision, dual-comb spectroscopy in methanol and ethanol vapor. These results highlight the potential of laser frequency combs for wide-ranging molecular sensing applications, from basic molecular spectroscopy to nanoscopic imaging.