Surface-Enhanced Dual-Comb Coherent Raman Spectroscopy with Nanoporous Gold Films

With two asynchronous frequency combs beating on a single detector, dual-comb spectroscopy (DCS) enables rapid, broadband, and precise molecular fingerprinting on a comb tooth-by-tooth basis and thus holds much promise in molecular sensing. Sensitivity, however, has been an Achilles’ heel of this technique. Here, an approach for ultrasensitive nonlinear DCS based on plasmon-enhanced coherent Raman spectroscopy (CRS) with ultrathin (100 nm) nanoporous gold films is presented. A high-resolution (<8 cm⁻¹) Raman spectrum is obtained within 32.8 µs for characterizing low-density chemicals. The achieved sensitivity enhancement reaches ≈10^6–8 relative to nonenhanced dual-comb CRS of liquid samples. The demonstrated approach may open up a new avenue for fast identification of trace amounts of chemicals.