title: Bright-white beetle scales optimise multiple scattering of light.
abstract: Whiteness arises from diffuse and broadband reflection of light typically achieved through optical scattering in randomly structured media. In contrast to structural colour due to coherent scattering, white appearance generally requires a relatively thick system comprising randomly positioned high refractive-index scattering centres. Here, we show that the exceptionally bright white appearance of Cyphochilus and Lepidiota stigma beetles arises from a remarkably optimised anisotropy of intra-scale chitin networks, which act as a dense scattering media. Using time-resolved measurements, we show that light propagating in the scales of the beetles undergoes pronounced multiple scattering that is associated with the lowest transport mean free path reported to date for low-refractive-index systems. Our light transport investigation unveil high level of optimisation that achieves high-brightness white in a thin low-mass-per-unit-area anisotropic disordered nanostructure.
authors.affiliation: 1] European Laboratory for Non-linear Spectroscopy (LENS), Università di Firenze, 50019 Sesto Fiorentino (FI), Italy [2] Istituto Nazionale di Ottica (CNR-INO), Largo Fermi 6, 50125 Firenze (FI), Italy.
authors.forename: Matteo
authors.initials: M
authors.lastname: Burresi
authors.affiliation: 1] European Laboratory for Non-linear Spectroscopy (LENS), Università di Firenze, 50019 Sesto Fiorentino (FI), Italy [2] Università di Firenze, Dipartimento di Fisica e Astronomia, 50019 Sesto Fiorentino (FI), Italy.
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Cortese
authors.affiliation: 1] European Laboratory for Non-linear Spectroscopy (LENS), Università di Firenze, 50019 Sesto Fiorentino (FI), Italy [2] Università di Firenze, Dipartimento di Fisica e Astronomia, 50019 Sesto Fiorentino (FI), Italy.
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Pattelli
authors.affiliation: School of Engineering and Applied Sciences Harvard University 29 Oxford St., Cambridge, MA, 02138, USA and Department of Mechanical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA.
authors.forename: Mathias
authors.initials: M
authors.lastname: Kolle
authors.affiliation: Thin Film Photonics, School of Physics, Exeter University, Exeter EX4 4QL, UK.
authors.forename: Peter
authors.initials: P
authors.lastname: Vukusic
authors.affiliation: 1] European Laboratory for Non-linear Spectroscopy (LENS), Università di Firenze, 50019 Sesto Fiorentino (FI), Italy [2] Università di Firenze, Dipartimento di Fisica e Astronomia, 50019 Sesto Fiorentino (FI), Italy.
authors.forename: Diederik S
authors.initials: DS
authors.lastname: Wiersma
authors.affiliation: Cavendish Laboratory, Department of Physics, University of Cambridge, J. J. Thomson Avenue, Cambridge CB3 0HE, U.K.
authors.forename: Ullrich
authors.initials: U
authors.lastname: Steiner
authors.affiliation: 1] Cavendish Laboratory, Department of Physics, University of Cambridge, J. J. Thomson Avenue, Cambridge CB3 0HE, U.K [2] Department of Chemistry, University of Cambridge Lensfield Road, Cambridge CB2 1EW UK.
authors.forename: Silvia
authors.initials: S
authors.lastname: Vignolini
mesh_terms: D000818:Animals; D016880:Anisotropy; D002686:Chitin / Q000378:metabolism*; D001517:Coleoptera / Q000502:physiology*; D003116:Color; D008027:Light; D012031:Refractometry; D012542:Scattering, Radiation
chemical_list: D002686:Chitin