Observation of the splitting of degenerate surface plasmon polariton modes in a two-dimensional metallic nanohole array

The authors report the experimental observation of the splitting of the degenerate (0,±1) surface plasmon polariton modes excited in a metallic nanohole array integrated with microfluidic channel for delivery and precise control of the index of refraction of overlaying layer. They use high-resolution wavelength and angle scans for excitation of the surface modes and a polarizer-analyzer pair to suppress the nonresonant transmission. The two resultant modes include an intense, spectrally broad low-energy mode and a weaker, much narrower bandwidth high-energy mode.