Flexible Electro-Optic, Single-Crystal Difference Frequency Generation Architecture for Ultrafast Mid-Infrared Dual-Comb Spectroscopy

Crowded with the fundamental signatures of many popular molecules, the mid-infrared range of the electromagnetic spectrum is particularly attractive for applications ranging from identification of transient phenomena to sensing of trace gases. Dual-comb spectroscopy is a technique that unveils the potential to access this region with a pair of phase-locked optical frequency combs on a high-resolution, real-time basis without the mechanical limitations of traditional spectrometers. As the ideal characteristics of an optical frequency comb are strongly influenced by the target application, electro-optic dual-comb systems are one of the most promising solutions with full capabilities to neatly fit to the application of interest beyond laboratory environments. Parameters such as resolution, measurement speed, or central wavelength are easily adjustable by means of compact, low-cost arrangements based on commercial off-the-shelf components. To fully exploit their potential for molecular spectroscopy, we present here a modular instrument designed to perform ultrafast dual-comb spectroscopy in the mid-infrared region. The architecture comprises a fiberized near-infrared electro-optic dual-comb scheme and a single-crystal difference frequency generation module to generate mid-infrared combs, thus significantly alleviating the complexity of the free-space setup while preserving absolute independence between the instrument and the sample of study. The feasibility of the instrument is successfully validated by recovering the absorption profile of methane at 2896.98 cm–1 within tens of microseconds.