SPR Optical Module (Surface Plasmon Resonance)

Surface Plasmon Resonance(SPR) is the resonant oscillation of
conduction electrons at the interface between a negative and
positive permittivity material stimulated by incident light.

The resonance condition is established when the frequency of
incident photons matches the natural frequency of surface electrons oscillating against the restoring force of positive nuclei.

SPR is the basis of many standard tools for measuring absorption of material on to planar metal(typical y gold and silver) surfaces or on to the surface of metal nanoparticles.

The SPR effect is useful because any change in the dielectric constant will result in a change in the resonance angle.