Detailed experimental analysis of the structural fluorescence in the butterfly Morpho sulkowskyi (Nymphalidae)
Résumé
The Morpho sulkowskyi concentrates on its dorsal wings complementary features contributing to its visual attraction: predominantly translucent, their wings display a blue coloration due to light interference. Fluorescent molecules, producing a violet-blue coloration when irradiated by ultraviolet light, are embedded in the scales which present a two-dimensional photonic structure. We investigate i. the effects of the fluorophores confinement in the structure on the variation of the emission intensity and coloration with the observation direction and ii. the correlation between the reflection and emission processes that control the surface optical response. Three types of measurements have been carried out. The morphology of the butterfly was examined with a scanning electron microscope. Then, the spatial distribution of the reflected light was measured with a viewing angle instrument, providing bidirectional reflectance distribution function data. Finally, an automatic method coupling an ultraviolet source to a gonio-spectrophotometer allowed for an extensive fluorescent emission characterization and provided angular emission maps. We find a spatial variation of the emission intensity and coloration and also an exhaustion behavior of the fluorophores. Moreover, we reveal that the spatial distribution of the emitted and reflected light is mainly governed by the photonic structure. (C) 2011 Society of Photo-Optical Instrumentation Engineers (SPIE). [DOI: 10.1117/1.3659147]