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 106–8 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.
Figure. a) The dual-comb SECARS interferogram and b) the Fouriertransformed spectra. The zoom-in of the interferogram with 60× enlargement of y-axis is shown in the inset of (a). In (b), the spectrum of single measurement is taken in 32.8 μs with an apodized resolution of 8 cm−1.
