Enhanced ultrafast infrared spectroscopy using coupled nanoantenna arrays.

Surface-enhanced nonlinear vibrational spectroscopy using periodic gold nanoantenna arrays is demonstrated. The dipolar coupling among arrayed nanoantennas is shown to have striking impact on near-field enhancements of femtosecond pulsed-fields and on nonlinear signal enhancements. The condition near the collective-resonance achieves averaged signal enhancement of 850 times and local signal enhancement of 1.8 × 10 times, substantially reducing the required pump energy from micro-joule to nano-joule level. The scheme is useful for characterizing structure and dynamics of minute-volume molecular samples, monolayers, and interfaces, as well as paves the way to nonlinear vibrational spectroscopy with compact light sources of oscillator-level.