SNOM Observations of Surface Plasmon Polaritons on Metal Heterostructures

We observe surface plasmon polariton (SPP) refraction on a metal heterostructured sample with a scattered-type scanning near-field optical microscope (SNOM). The sample consists of Al and Au in-plane whose boundary is smooth enough with proper etching time. SPPs excited on the Al film travel to the boundary and a portion of SPPs propagates into the Au film. In addition, interference fringes appear in the SNOM image bent at the boundary. The result is analysed with effective index method and the refracted angle is explained by Snell's law.