Dual-comb spectroscopy using plasmon-enhanced-waveguide dispersion-compensated quantum cascade lasers

In this Letter, we report on sub-millisecond response time mid-infrared dual-comb spectroscopy using a balanced asymmetric (dispersive) dual-comb setup with a matched pair of plasmon-enhanced-waveguide dispersion-compensated quantum cascade lasers. The system performance is demonstrated by measuring spectra of Bromomethane (CH₃Br) and Freon 134a (CH₂FCF₃) at approximately 7.8 μm. A purely computational phase and timing-correction procedure is used to validate the coherence of the quantum cascade lasers frequency combs and to enable coherent averaging over the time scales investigated. The system achieves a noise-equivalent absorption better than 1 × 10−³ Hz⁻¹∕², with a resolution of 9.8 GHz (0.326 cm⁻¹) and an optical bandwidth of 1 THz (32 cm⁻¹), with an average optical power of more than 1 mW per spectral element.