Fig. 3.

Characterization of a subwavelength SPPs focus in a Sb₂Te₃ thin film. a SEM image of the fabricated ultrathin plasmonic lens. b Simulated intensity distribution of the plasmonic focus excited by the plasmonic lens. The arrow shows the orientation of linearly polarized incident light. c Experimentally measured intensity distribution of the plasmonic focus by a SNOM system. d The cross-section of the measured intensity distribution of the plasmonic focus. The wavelength of the incident light beam is 640 nm. The period of the interference fringes of evanescent SPPs standing waves is around 305 nm which suggests the SPPs wavelength of 610 nm in the SNOM characterization