Total Internal Reflection Accounts for the Bright Color of the Saharan Silver Ant.

The Saharan silver ant Cataglyphis bombycina is one of the terrestrial living organisms best adapted to tolerate high temperatures. It has recently been shown that the hairs covering the ant's dorsal body part are responsible for its silvery appearance. The hairs have a triangular cross-section with two corrugated surfaces allowing a high optical reflection in the visible and near-infrared (NIR) range of the spectrum while maximizing heat emissivity in the mid-infrared (MIR).

Radiative contribution to thermal conductance in animal furs and other woolly insulators.

This paper deals with radiation's contribution to thermal insulation. The mechanism by which a stack of absorbers limits radiative heat transfer is examined in detail both for black-body shields and grey-body shields. It shows that radiation energy transfer rates should be much faster than conduction rates.

Method for modeling additive color effect in photonic polycrystals with form anisotropic elements: the case of Entimus imperialis weevil.

The calculation of the reflectance of photonic crystals having form-birefringent anisotropic elements in the crystal unit cell, such as cylinders, often turns out to be problematic, especially when the reflectance spectrum has to be computed according to different crystal orientations as in polycrystals for instance. The method we propose here solves this problem in the specific case of photonic crystals whose periodicities are such that there are no diffraction orders except Bragg reflection in the visible range. For a given crystal orientation, the crystal is sliced into layers and the periodic spatial variations of the dielectric function ε are homogenized.

Cylindrical Bragg mirrors on leg segments of the male Bolivian blueleg tarantula Pamphobeteus antinous (Theraphosidae).

The large male tarantula Pamphobeteus antinous is easily recognized at the presence of blue-violet iridescent bristles on some of the segments of its legs and pedipalps. The optical properties of these colored appendages have been measured and the internal geometrical structure of the bristles have been investigated. The coloration is shown to be caused by a curved coaxial multilayer which acts as a "cylindrical Bragg mirror".

Optimal overlayer inspired by Photuris firefly improves light-extraction efficiency of existing light-emitting diodes.

In this paper the design, fabrication and characterization of a bioinspired overlayer deposited on a GaN LED is described. The purpose of this overlayer is to improve light extraction into air from the diode's high refractive-index active material. The layer design is inspired by the microstructure found in the firefly Photuris sp.

Improved light extraction in the bioluminescent lantern of a Photuris firefly (Lampyridae).

A common problem of light sources emitting from an homogeneous high-refractive index medium into air is the loss of photons by total internal reflection. Bioluminescent organisms, as well as artificial devices, have to face this problem. It is expected that life, with its mechanisms for evolution, would have selected appropriate optical structures to get around this problem, at least partially.

Bi-functional photonic structure in the Papilio nireus (Papilionidae): modeling by scattering-matrix optical simulations.

Scales of the Papilio nireus combine fluorophores confined in a natural photonic structure. By means of numerical simulations based on the scattering-matrix formalism, we reveal the bi-functional optical role of this peculiar architecture. Two aspects are considered: the absorption of an incident light flux and the emission of another luminous flux.

Photonic polycrystal in the greenish-white scales of the African longhorn beetle Prosopocera lactator (Cerambycidae).

Three-dimensional photonic-crystal grains were found in the scales of the longhorn beetle Prosopocera lactator (Cerambycidae). The local geometric structure can be described as a face-centered-cubic array of spheres, connected by short rods, reminiscent of the "ball-and-stick" models used by solid-state chemists to visualize atomic structures. Based on scanning electron microscopy, x-ray nanotomography, optical measurements, photonic band-structure calculations, and computer simulations of the reflectance, the desaturated greenish coloration is shown to arise from the observed photonic polycrystalline structure.

Structural color produced by a three-dimensional photonic polycrystal in the scales of a longhorn beetle: Pseudomyagrus waterhousei (Coleoptera: Cerambicidae).

The cuticle of the longhorn beetle Pseudomyagrus waterhousei shows a diffuse pattern of mixed blue and violet colors. These colorations arise from a dense layer of droplet-shaped scales covering the dorsal parts of the cuticle. In spite of their lack of iridescence, these colors are shown to be structural and produced by an aggregate of internally ordered photonic-crystal grains.

Reverse color sequence in the diffraction of white light by the wing of the male butterfly Pierella luna (Nymphalidae: Satyrinae).

The butterfly Pierella luna (Nymphalidae) shows an intriguing rainbow iridescence effect: the forewings of the male, when illuminated along the axis from the body to the wing tip, decompose a white light beam as a diffraction grating would do. Violet light, however, emerges along a grazing angle, near the wing surface, while the other colors, from blue to red, exit respectively at angles progressively closer to the direction perpendicular to the wing plane. This sequence is the reverse of the usual decomposition of light by a grating with a periodicity parallel to the wing surface.

Scale coloration change following water absorption in the beetle Hoplia coerulea (Coleoptera).

The blue scales on the cuticle of the male beetle Hoplia coerulea can absorb water, with the consequence that these scales, which have been shown to be responsible for the beetle's bright blue coloration, reversibly turn to emerald green with increasing water contents. Optical measurements are shown, by analytic photonic-crystal models, to be compatible with the full filling of the scales structures with water. The natural mechanism shows the way to produce a very efficient hygrochromic material: a medium which significantly changes color when its water contents are modified.

Assessment of the antireflection property of moth wings by three-dimensional transfer-matrix optical simulations.

The wings of the moth Cacostatia ossa (Ctenuchinae) are covered on both sides by non-close-packed nipple arrays which are known to act as broadband antireflection coatings. Experimental evaluation of the antireflection property of these biological structures is problematic because of the lack of a proper reference for reflectance measurements, i.e.

An epicuticular multilayer reflector generates the iridescent coloration in chrysidid wasps (Hymenoptera, Chrysididae).

Chrysidid wasps in the subfamily Chrysidinae are brood parasitoids or cleptoparasites of other insects and famous for their cuticular iridescence. In this study, we examine the dorsal abdominal cuticle of the chrysidid wasp Hedychrum rutilans to identify the underlying color mechanism. Using scanning electron microscopy, reflectance spectral analysis, and theoretical calculations, we demonstrate the presence of an epicuticular multilayer reflector consisting of six lamellae with a thickness of 185 nm each.

Spectral sideband produced by a hemispherical concave multilayer on the African shield-bug Calidea panaethiopica (Scutelleridae).

The African shield-backed bug Calidea panaethiopica is a very colorful insect which produces a range of iridescent yellow, green, and blue reflections. The cuticle of the dorsal side of the insect, on the shield, the prothorax and part of the head, is pricked of uniformly distributed hemispherical hollow cavities a few tens micrometers deep. Under normal illumination and viewing the insect's muffin-tin shaped surface gives rise to two distinct colors: a yellow spot arising from the bottom of the well and a blue annular cloud that appears to float around the yellow spot.

Nanomorphology of the blue iridescent wings of a giant tropical wasp Megascolia procer javanensis (Hymenoptera).

The wings of the giant wasp Megascolia procer javanensis are opaque and iridescent. The origin of the blue-green iridescence is studied in detail, using reflection spectroscopy, scanning electron microscopy, and physical modeling. It is shown that the structure responsible for the iridescence is a single homogeneous transparent chitin layer covering the whole surface of each wing.

Composite organic-inorganic butterfly scales: production of photonic structures with atomic layer deposition.

Recent advances in the photonics and optics industries have produced great demand for ever more sophisticated optical devices, such as photonic crystals. However, photonic crystals are notoriously difficult to manufacture. Increasingly, therefore, researchers have turned towards naturally occurring photonic structures for inspiration and a wide variety of elaborate techniques have been attempted to copy and harness biological processes to manufacture artificial photonic structures.

Correlated diffraction and fluorescence in the backscattering iridescence of the male butterfly Troides magellanus (Papilionidae).

The male Troides magellanus--a birdwing butterfly that lives in a restricted area of the Philippines--concentrates on its hindwings at least two distinct optical processes that contribute to its exceptional visual attraction. The first is the very bright uniform yellow coloration caused by a pigment which generates yellow-green fluorescence, and the other is a blue-green iridescence which results from light diffraction at grazing emergence under a specific illumination. Detailed optical measurements reveal that these optical effects are correlated, the fluorescence being enhanced by illuminations conditions that favor the occurrence of the iridescence.

Report. Dual gratings interspersed on a single butterfly scale.

Iridescent butterfly wing colours result from the interaction of light with sub-micrometre structures in the scales. Typically, one scale contains one such photonic structure that produces a single iridescent signal. Here, however, we show how the dorsal wings of male Lamprolenis nitida emit two independent signals from two separate photonic structures in the same scale.

Switchable reflector in the Panamanian tortoise beetle Charidotella egregia (Chrysomelidae: Cassidinae).

The tortoise beetle Charidotella egregia is able to modify the structural color of its cuticle reversibly, when disturbed by stressful external events. After field observations, measurements of the optical properties in the two main stable color states and scanning electron microscope and transmission electron microscope investigations, a physical mechanism is proposed to explain the color switching of this insect. It is shown that the gold coloration displayed by animals at rest arises from a chirped multilayer reflector maintained in a perfect coherent state by the presence of humidity in the porous patches within each layer, while the red color displayed by disturbed animals results from the destruction of this reflector by the expulsion of the liquid from the porous patches, turning the multilayer into a translucent slab that leaves an unobstructed view of the deeper-lying, pigmented red substrate.

Orange reflection from a three-dimensional photonic crystal in the scales of the weevil Pachyrrhynchus congestus pavonius (Curculionidae).

The three-dimensional structure that causes the coloration of the tropical weevil Pachyrrhynchus congestus pavonius was studied, using a combination of electron microscopy, optical spectroscopy, and numerical modeling. The orange scales that cover the colored rings on the animal's body were opened, to display the structure responsible for the coloration. This structure is a three-dimensional photonic polycrystal, each grain of which showing a face-centered cubic symmetry.

Wide angular range operation of a dielectric multilayer film with a photonic-crystal-type defect.

Light can tunnel through a high-reflectivity dielectric multilayer film when a photonic-crystal-type defect is introduced in the structure, which is useful for optical signal processing. We consider chirped structures with a defect in layer thickness for which high reflectivity is achieved over a broad wavelength range except within a narrow spectral window. The useful transmission window, while it shifts toward shorter wavelengths as the angle of incidence of the light beam is increased, does not, in general, survive; i.

Gleaming and dull surface textures from photonic-crystal-type nanostructures in the butterfly Cyanophrys remus.

Photonic-crystal-type nanostructures occurring in the scales of the butterfly Cyanophrys remus were investigated by optical and electron microscopy (scanning and transmission electron microscopy), reflectance measurements (specular, integrated, and goniometric), by fast Fourier transform analysis of micrographs, by modeling, and by numerical simulation of the measured reflectance data. By evaluating the collected data in a cross-correlated way, we show that the metallic blue dorsal coloration originates from scales which individually are photonic single crystals of 50 x 120 microm2 , while the matt pea-green coloration of the ventral side arises from the cumulative effect of randomly arranged, bright photonic crystallites (blue, green, and yellow) with typical diameters in the 3-10-mum range. Both structures are based on a very moderate refractive index contrast between air and chitin.

Optical properties of the iridescent organ of the comb-jellyfish Beroë cucumis (Ctenophora).

Using transmission electron microscopy, analytical modeling, and detailed numerical simulations, the iridescence observed from the comb rows of the ctenophore Beroë cucumis was investigated. It is shown that the changing coloration which accompanies the beating of comb rows as the animal swims can be explained by the weakly-contrasted structure of the refractive index induced by the very coherent packing of locomotory cilia. The colors arising from the narrow band-gap reflection are shown to be highly saturated and, as a function of the incidence angle, cover a wide range of the visible and ultraviolet spectrum.

Spectral filtering of visible light by the cuticle of metallic woodboring beetles and microfabrication of a matching bioinspired material.

Samples of the cuticle taken from the body of Buprestidae Chrysochroa vittata have been studied by scanning electron microscopy and optical reflectance measurements, related to numerical simulations. The cause of the metallic coloration of the body of these insects is determined to be the structure of the hard carapace constructed as a stack of thin chitin layers separated by very thin irregular air gaps. In particular the change of color as a function of the observation angle is elucidated in terms of an infinite photonic-crystal model, confirmed by finite multilayer calculations.