Optical Characterization of Iridescent Wings of <Emphasis Type="Italic">Morpho</Emphasis> Butterflies using a High Accuracy Nonstandard Finite-Difference Time-Domain Algorithm |
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Authors: | Saswatee Banerjee Zhu Dong |
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Institution: | (1) Sumitomo Chemical Co. Ltd., Tsukuba Ibaraki, 300-3294, Japan;(2) Graduate School of Systems and Information Engineering, University of Tsukuba, Ibaraki, 305-8577, Japan |
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Abstract: | In certain species of moths and butterflies iridescent colors arise from subwavelength diffractive surface corrugation of
the wing-scales. The optical properties of such structures depend strongly on wavelength, incidence angle, and state of polarization
of illuminating radiation, and the viewing angle. In this paper, we study the reflection spectra of the wings of the Morpho didius butterfly by simulating a double-layered model of a transverse cross-section comprised of the ground scale and the cover
scale. Each layer contains a certain quasi-periodic arrangement of tree-like subwavelength microstructures. The simulation
is done using a high accuracy nonstandard finite-difference time-domain (FDTD) method in two dimensions. We assume that the
structure is made of a slightly lossy dielectric material. The wavelength dependence of the complex refractive index for the
ground scale of Morpho didius is assumed to be similar to that of Morpho sulkowskyi. The complex refractive index in the latter case was obtained by comparing the computed reflection/transmission spectra with
corresponding experimental measurements at normal incidence. |
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Keywords: | Morpho butterflies butterfly iridescence structural color subwavelength diffractive optical elements gratings and diffraction interference electromagnetic theory finite-difference time-domain method |
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