Surface plasmon resonances (SPRs) are collective oscillations of free electrons at the interface between a metal and a dielectric material, such as air or water. These oscillations occur when the frequency of incident light matches the natural frequency of surface electrons oscillating against the restoring force of positive nuclei. This phenomenon is particularly prominent at the nanoscale, where the interaction of light with metal nanoparticles can generate strong electromagnetic fields at specific resonant frequencies.
