Smart strategy of butterfly wing scales to control the light diffusion and absorption

Abstract

The sparkling colors on the wing scales of butterflies are one of the most fascinating light–matter interactions in nature and have been an intense area of research in recent times. Controlling the light diffusion and absorption due to multiple scattering induced by the inherent disorder in the wing scales is required for applications in imaging, light trapping, and localization using such bio-inspired photonic structures. Here, we study the selective anisotropic light diffusion and absorption in the nanoarchitectures of Pieris rapae and Graphium sarpedon butterfly wing scales in the visible range. We have measured broadband spatially independent low values of specular reflectivity and ballistic transmission from the ventral and the dorsal sides of the wing scales, which are supported with finite-difference time-domain simulations. The specular reflectivity value as small as 3% indicates strong diffuse scattering within the scales, probed using total transmission and reflection measurements. We have found finite wavelength-dependent absorption <100% in these wing scales. Further, we have obtained negative scattering anisotropy (g ) values from the dorsal side, whereas it is positive from the ventral side for both butterflies. The negative g value originating due to the inherent structural correlation is differentiated from that arising due to pigment absorption. The results are useful for generating the optimized light scattering in bio-inspired photonic devices.