Metasurface-enhanced mid-infrared imaging spectroscopy with broadband quantum cascade lasers

Mid-infrared spectroscopy offers unparalleled opportunities in sensing through chemically specific detection of molecular absorption fingerprints. Yet its practical applications are limited by weak light-matter interaction and complex and relatively slow instrumentation relying on scanning components. Here, we develop a rapid imaging-based mid-IR spectroscopy platform that combines broadband resonance gradient metasurfaces and radiofrequency-modulated quantum cascade laser generating broad (250 cm^-1) instantaneous spectrum. We match the resonance spectrum of the gradient metasurface with the laser emission for targeted amplification of local electromagnetic field of all its spectral components. This enables capturing of enhanced absorption signatures of analytes deposited on the metasurface as barcode images in a single shot of room-temperature low-cost mid-infrared camera, reducing the acquisition time by up to 3 orders of magnitude compared to measurements with Fourier-transform infrared spectrometers and external cavity quantum cascade lasers. Eliminating the need for tunable light sources, bulky spectrometers, and expensive low-temperature detectors, our approach enables high-throughput, miniaturized, and highly specific molecular diagnostics for diverse chemical and biological applications.