Refractive index and thickness determination of monolayers by multi mode waveguide coupled surface plasmons

Abstract

The coupling of p-polarized waveguide modes into waveguide-surface plasmon coupled modes is a promising concept to combine the features of propagating waveguide modes with the resonant field enhancement of surface plasmons. We demonstrate a waveguide device which allows to couple two TM modes to the surface plasmon. For a given waveguide device and a fixed laser wavelength the development of the imaginary part, κ, of the propagation constant, N eff, of the waveguide-surface plasmon coupled modes are simulated to optimize a monolayer sensitive device. The waveguide attenuation is very sensitive to the refractive index architecture within the evanescent field of these combined modes. This resonant behavior was used to measure the refractive index and the geometrical thickness of self-assembled monolayers independently from each other. In addition the binding of uracil to a binary monolayer containing adenin was investigated.