Demonstration of higher colour response with ambient refractive index in Papilio blumei as compared to Morpho rhetenor

Multilayer structures are known to produce vivid iridescent colouration in many butterflies. Morpho butterflies are well known for their high reflectance, which appears to remain high over a wide range of viewing angles. Thus these butterflies have served as the inspiration for sensing materials. Using microscopic images and videos, we visually demonstrate that the colour response with ambient refractive index of Papilio blumei is better than that of Morpho rhetenor. This result was also verified using measurements of the reflectance for different viewing angles. The finite-difference time-domain method was then used to simulate the microscopic pictures and reflections. Finally, the relationships between the structure, ambient refractive index, reflection and viewing angle are discussed in detail.