Single-scale spectroscopy of structurally colored butterflies : measurements of quantified reflectance and transmittance

Butterfly scales generally have very elaborate structures in submicrometer size, and some of them show distinctive optical effects through interaction with light. We describe two methods to quantitatively characterize the optical properties of the individual scales in those structurally colored butterflies. Owing to the small dimensions of the scale and to the fact that the reflection and transmission are very diffuse, it is generally difficult to accurately measure the reflectance and transmittance. To overcome these difficulties, we have carefully constructed an optical system including an integrating sphere and investigated variously colored nine kinds of scale. It is shown that the obtained spectra clearly characterize the optical differences among those structurally colored scales and also the differences between structural and pigmentary colors. Further, we have performed the angle-resolved measurement of the reflected light to characterize the spatial pattern of reflection, which is closely related to the mechanism of reflection.