Mid-infrared optical frequency combs based on difference frequency generation for molecular spectroscopy

Mid-infrared femtosecond optical frequency combs were produced by difference frequency generation of the spectral components of a near-infrared comb in a 3-mm-long MgO:PPLN crystal. We observe strong pump depletion and 9.3 dB parametric gain in the 1.5 mu m signal, which yields powers above 500 mW (3 mu W/mode) in the idler with spectra covering 2.8 mu m to 3.5 mu m. Potential for broadband, high-resolution molecular spectroscopy is demonstrated by absorption spectra and interferograms obtained by heterodyning two combs. (C) 2015 Optical Society of America