Figure 1. Kretschmann configuration and key parameters obtained from the full SPR angular spectra.

A) A simplified chart of the Kretschmann configuration enabling plasmon excitations and SPR measurements. The intensity of the reflected light from a monochromatic light source is measured as a function of incident light angle (θ). The light passes from a high refractive index medium (glass, ε₀) to a low refractive index medium (air or liquid, ε₁+ε_bulk). In between, the light is reflected from an interface containing a metal with a high density of free electrons and an optimal thickness for plasmon excitation (gold 50 nm, ε₂) to a photodetector. The surface plasmons on the metal surface are excited at a certain incident light angle (θ) and the evanescent field created by the plasmon extends to the adjacent low refractive index medium (ε₁) where samples are introduced to the system. B) A schematic full SPR angular spectrum showing the positions of the TIR region, the main SPR peak angular position and the main SPR peak minimum intensity.