Real part of the dielectric constant of a subwavelength-in-diameter silver pipe is positive in visible light

The complex refractive index of a silver pipe of which the diameter is subwavelength in diameter have been found to be different from those of a silver thin film for the first time. The silver pipe is made of cladding a spider silk of a half-wavelength diameter with silver. It is illuminated by a plane-polarized laser of wavelength 660 nm at normal incidence. The angular distribution of the light intensity scattered by the pipe is measured and fitted using theoretical calculations based on the corresponding model. The fitting results have led to the optimum values and uncertainty ranges of the index and the diameter of the pipe.