Visually identifying the refractive index using surface plasmons excited by white-light

Optical waves can induce collective oscillations of free electrons on a metal surface and propagate on the surface under specific conditions. These waves are known as surface plasmon polaritons (SPPs). SPPs are implemented in sensors because their excitation is affected by the refractive index of the surface medium. When SPPs are excited on a metal film in a Kretschmann configuration, they are indirectly detected through the difference between the incident and reflected light because SPPs are non-radiative surface waves. We scattered SPPs to directly observe them using a rough surface. Accordingly, we discussed the corresponding resolution characteristics and influence of roughness on the SPP excitation. Our method allows to quickly take two-dimensional images of samples because scattered waves from the surface can be observed using conventional imaging optics.