Reflections on iridescent neck and breast feathers of the peacock, Pavo cristatus

Abstract

One contribution of 11 to a theme issue 'Living light: optics, ecology and design principles of natural photonic structures'.The blue neck and breast feathers of the peacock are structurally coloured due to an intricate photonic crystal structure in the barbules consisting of a two-dimensionally ordered rectangular lattice of melanosomes (melanin rodlets) and air channels embedded in a keratin matrix. We here investigate the feather coloration by performing microspectrophotometry, imaging scatterometry and angle-dependent reflectance measurements. Using previously determined wavelength-dependent refractive indices of melanin and keratin, we interpret the spectral and spatial reflection characteristics by comparing the measured spectra to calculated spectra by effective-medium multilayer and full three-dimensional finite-difference time-domain modelling. Both modelling methods yield similar reflectance spectra indicating that simple multilayer modelling is adequate for a direct understanding of the brilliant coloration of peacock feathers.

Optical costs and benefits of disorder in biological photonic crystals

“…Here, melanin rodlets (called melanosomes), arranged in a square array, sit in a keratin matrix (interlaced with air gaps). 16,17,[170][171][172] The colours of all blue, green, yellow and orange neck and breast feathers are caused by identical optical effects in the observed 2D photonic crystals. The difference in reected hue simply arises from different periodicities, typically 150 nm for blue feathers and closer to 190 nm for the yellow and green feathers.…”

“…16,17,170 More recently, it was shown that simple effective-medium multilayer modelling is suited to modelling these feather colour appearances. 171,172 To analyse the extent of order or disorder in these systems, a Delaunay triangulation algorithm 173 was applied to TEM images of the cross-sections of these structures and the avian dermal structures studied by Prum et al (Fig. 13 and 14), using the method described in ref.…”

Biophotonics of diversely coloured peacock tail feathers

“…Effective-medium theory for two-phase nanostructures predicts weighting factors w TE ¼ 2 and w TM ¼ À2 for TE (Transverse Electric)-and TM (Transverse Magnetic)polarised light, respectively. [41][42][43] However, in our previous study on the multilayered blue neck and breast feathers of the peacock, we compared reectance and absorbance spectra modelled with the effective-medium multilayer approach with spectra obtained with the nite-difference time-domain (FDTD) method 31 and found a close correlation when the effective-medium multilayer calculations were performed with slightly modied weighting factors: w TE ¼ 2.5 and w TM ¼ À1.5. We therefore used these adjusted weighting factors in the present study.…”

“…The measured spectra could be well explained with an effective-medium multilayer model. 31 Extending this approach, here we present a detailed set of reectance spectra of the tail feathers with a comprehensive analysis of the feathers' rich colouration pattern, using recently determined refractive index values of bird keratin and melanin. 16,32 We include all six colour regions that were characterized by Durrer 1,4,5 and highlight the key optical parameters that determine the reectance band shape.…”

Bio-Inspired Self-Adhesive Bright Non-iridescent Graphene Pigments

“…This characteristic brightness is derived from their specific microstructure and the existence of melanosomes, which provide the high refractive index and broadband light absorption. [26][27][28][29] To mimic this phenomenon, various dark elements have been applied to enhance the saturation of the structural colors. Among these elements, GO has significant features of high refractive index, good photothermal effect, relatively large specific surface area, and abundant functional groups on the surface.…”