Determination of the Complex Refractive Index of a Subwavelength-diameter Spider Thread on Silver Coating by Light Scattering

Abstract

In this study, we have created nano-scale silver pipes by sputtering the silver material which frequently shows negative or less-than 1 refractive index onto the spider thread thinner than optical wavelength with. As a part of the study to investigate distribution of the complex refractive index which indicates optical and electromagnetic properties of the resulting silver pipes, we used light scattering method using linearly polarized laser with wavelength of 660 nm and radiated it perpendicularly to the silver pipe to measure the angular distribution of the scattered light intensity. Using the numerical calculation with Coaxial cylinder model based on the values found through preceding studies, we calculated the angular distribution of the scattered light intensity, and fitted the calculation result to the measurement result. This allowed us to determine the complex refractive index and outer diameter of the silver pipe along with the error range. The silver pipe was observed with field emission scanning electron microscope (FE-SEM) and the outer diameter of the silver pipe was estimated. This outer diameter was compared with the outer diameter obtained by fitting the calculation result with the light scattering method to the measurement result to evaluate the validity of the measurement result. This revealed that the result obtained with light scattering method has showed good agreement with that measured using FE-SEM.