Strong interaction of molecular vibrational overtones with near-guided surface plasmon polariton

摘要

Here, we report on the enhancement of molecular vibrational transitions overtones due to the excitation of surface plasmon polariton waves. We show that, assuming a modified Kretschmann-Reather configuration with ultra-thin dielectric over-layer, the effective absorption cross section of higher harmonics of molecular vibrations is boosted by at least two orders of magnitude. Based on the experimental observations reported by Karabchevsky and Kavokin on photonic waveguides, we calculate the differential absorption which appears to exhibit a Fano-like line shape. This manifests the interaction between a narrow molecular resonance and a broad plasmonic mode. In fact, the interaction occurs due to the highest enhancement of the vibrational transitions overtones when the vibration mode and plasmonic mode are detuned. The enhancement factor reported in this study points on feasibility of vibrational overtones detection using conventional spectrometers. In addition, having high signal-to-noise ratio opens a new route for molecular detection and sensing.