When light interacts with a metallic nanoparticle, it induces a collective oscillation of the conduction electrons at the surface of the particle. This collective oscillation is called a surface plasmon. At the resonance frequency, the amplitude of these oscillations is maximized, leading to a significant increase in the local electromagnetic field. This enhanced field can be used to manipulate light at the nanoscale, which is crucial for various applications in nanotechnology.
