We demonstrate the development of broadband, infrared frequency combs tunable from 3 to 27 microns. The source is based on using a robust, few-cycle Er:fiber comb (10 fs pulse duration) to drive intra-pulse difference frequency generation within a quasi-phase-matched nonlinear medium (e.g. periodically poled lithium niobite or orientation patterned gallium phosphide). Since the down-converted light has a longer optical period, the electric field of this longer wave light can be directly sampled by the few-cycle Er:fiber pulse via electro-optic sampling (EOS), directly yielding spectroscopic information on the infrared light. Further, by implementing EOS in a dual frequency comb configuration, we can increase the spectroscopic acquisition speed to a rate of 50 Hz. This dual-comb EOS configuration enables a measurement bandwidth spanning 370 – 3300 cm^-1 with a resolution down to the 100 MHz (0.003 cm^-1) spacing of the infrared comb. Due to the brightness of this comb source and the broad acquisition bandwidth, we can perform high resolution and high sensitivity spectroscopy on chemically and biologically relevant compounds spanning the molecular fingerprint region, with an outlook towards fast acquisition, infrared frequency comb microscopy.

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Henry Timmers, Abijith Kowligy, Alex Lind, Flavio C. Cruz, Ugaitz Elu, Peter Schunemann, Jens Biegert, and Scott Diddams, "Generation and detection of broadband infrared frequency combs spanning the molecular fingerprint region (Conference Presentation)," Proc. SPIE 10902, Nonlinear Frequency Generation and Conversion: Materials and Devices XVIII, 109020Y (Presented at SPIE LASE: February 06, 2019; Published: 4 March 2019); https://doi.org/10.1117/12.2514621.6008601226001.