Auxiliary Top‐Illumination in the Kretschmann–Raether Configuration: A Theoretical Study on the Surface Plasmon Resonance Response

Abstract

A new variation of surface plasmon resonance (SPR) sensors design with Kretschmann–Raether (KR)‐type configuration is presented. Using a rotational incident angle scanning platform, the conductor nanolayer is normally irradiated with an auxiliary unpolarized light beam from the dielectric side. Both illumination sources should have a coherence length much larger than their source/Au layer optical path. Beginning with a Lorentzian‐type oscillator model, a general dispersion equation for the metal nanolayer is developed that incorporates interband transitions and polychromaticity of the top‐illumination beam. SPR curves are then predicted based on the transfer‐matrix method. Simulation results show that the top‐illumination frequency and its relative amplitude with respect to the bottom laser beam may impart significant changes to the SPR curve. It is shown that the implementation of short‐wave ultraviolet light (180 nm) may considerably improve the performance of SPR sensors in terms of the figure‐of‐merit. Larger wavelengths generally lead to performance deterioration. Based on the transverse magnetic solutions of the wave equation, a theoretical interpretation of the results is presented that confirms the strong effect of top illumination on the magnitude of the decay lengths in the conductor/dielectric and the propagation constant.