Recent progress on mid-infrared and terahertz dual-comb spectroscopy

Dual-comb spectroscopy (DCS) has emerged as a revolutionary optical technique, offering exceptional spectral resolution, rapid measurement capability, and inherent frequency accuracy without the need for moving parts. This review provides a comprehensive survey of the principles and technological developments of DCS within the mid-infrared (mid-IR, ~2–20 μm) and terahertz (THz, ~0.1–10 THz) spectral regions. These regimes are of paramount importance due to the unique molecular fingerprints and low-energy excitations they encompass, spanning areas such as gas-phase chemical analysis, combustion diagnostics, and atmospheric sensing. We systematically outline the primary approaches for generating dual-comb sources in these spectral ranges, including direct generation via quantum cascade lasers, optical parametric oscillation, difference frequency generation, and microresonator-based frequency combs. The performance metrics, trade-offs, and recent innovations for each platform are critically compared. Finally, we discuss key challenges and emerging directions, including continuous mid-infrared-to-THz spectral coverage, broadband and low-noise detection, beam quality and mode matching, quantum-enhanced sensitivity, and coherence preservation for long-term operation. We conclude by outlining future trends toward integrated, field-deployable, and application-oriented DCS systems capable of broadband molecular fingerprinting, high-speed sensing, and precision spectroscopy.