Coherent frequency combs for spectroscopy across the 3-5 μm region

A tunable mid-infrared frequency comb was created via difference frequency generation. Pulses between 1 and 1.5 mu m were mixed to generate light ranging from 2.6 to 5.2 mu m. Two such combs were heterodyned at 5 mu m to show their coherence and potential for spectroscopy. The properties of the comb were modeled using numerical simulation, which confirmed the observed bandwidths.