Photophysics of Structural Color in the Morpho Butterflies

The Morpho butterflies exhibit surprisingly brilliant blue wings originating from the submicron structure created on scales of the wing. It shows extraordinarily uniform color with respect to the observation direction which cannot be explained using a simple multilayer interference model. We have performed microscopic, optical and theoretical investigations on the wings of four Morpho species and have found separate lamellar structure with irregular heights is extremely important. Using a simple model, we have shown that the combined action of interference and diffraction is essential for the structural color. It is also shown that the presence of pigment beneath the iridescent scales greatly enhances the blue coloring by reducing the unwanted background light. Further, variations of color tones and gloss in the Morpho wings are discussed in terms of the combination of cover and ground scales with various structures and functions.