Physical methods for investigating structural colours in biological systems

The neotropical diamond weevil, Entimus imperialis, is marked by rows of brilliant spots on the overall black elytra. The spots are concave pits with intricate patterns of structural-coloured scales, consisting of large domains of three-dimensional photonic crystals that have a diamond-type structure. Reflectance spectra measured from individual scale domains perfectly match model spectra, calculated with anatomical data and finite-difference time-domain methods. The reflections of single domains are extremely directional (observed with a point source less than 58), but the special arrangement of the scales in the concave pits significantly broadens the angular distribution of the reflections. The resulting virtually angle-independent green coloration of the weevil closely approximates the colour of a foliaceous background. While the closedistance colourful shininess of E. imperialis may facilitate intersexual recognition, the diffuse green reflectance of the elytra when seen at long-distance provides cryptic camouflage.

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“…We, therefore, used an imaging scatterometer (ISM), which is built around an ellipsoidal mirror [33,34].…”

Section: Methodsmentioning

confidence: 99%

Brilliant camouflage : photonic crystals in the diamond weevil, Entimus imperialis

et al. 2012

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“…The set-up shown in figure 1a is a slight modification of that described by Stavenga et al ([11]; see also [12,13]). The added facility, a CCD detector array spectrometer (SP; AvaSpec-2048-2, Avantes, Eerbeek, The Netherlands), samples a small area of the scattered light pattern via half-mirror H 2 , lens L 8 and one channel of a bifurcated light guide (effective aperture approx.…”

Section: (B) Anatomymentioning

confidence: 99%

Polarized iridescence of the multilayered elytra of the Japanese jewel beetle,Chrysochroa fulgidissima

Stavenga

Wilts

Leertouwer

et al. 2011

Phil. Trans. R. Soc. B

145

154

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The elytra of the Japanese jewel beetle Chrysochroa fulgidissima are metallic green with purple stripes. Scanning electron microscopy and atomic force microscopy demonstrated that the elytral surface is approximately flat. The accordingly specular green and purple areas have, with normal illumination, 100 -150 nm broad reflectance bands, peaking at about 530 and 700 nm. The bands shift progressively towards shorter wavelengths with increasing oblique illumination, and the reflection then becomes highly polarized. Transmission electron microscopy revealed that the epicuticle of the green and purple areas consists of stacks of 16 and 12 layers, respectively. Assuming gradient refractive index values of the layers between 1.6 and 1.7 and applying the classical multilayer theory allowed modelling of the measured polarization-and angle-dependent reflectance spectra. The extreme polarized iridescence exhibited by the elytra of the jewel beetle may have a function in intraspecific recognition.

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“…However, under epi-illumination, several additional optical components are necessary, as shown in figure 3. This type of optical apparatus is now called a microscatterometer [24]. The details of our setup are described below.…”

Section: Microscatterometermentioning

confidence: 99%

Mechanism of variable structural colour in the neon tetra: quantitative evaluation of the Venetian blind model

Yoshioka

Matsuhana

Tanaka

et al. 2010

J. R. Soc. Interface.

116

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The structural colour of the neon tetra is distinguishable from those of, e.g., butterfly wings and bird feathers, because it can change in response to the light intensity of the surrounding environment. This fact clearly indicates the variability of the colour-producing microstructures. It has been known that an iridophore of the neon tetra contains a few stacks of periodically arranged light-reflecting platelets, which can cause multilayer optical interference phenomena. As a mechanism of the colour variability, the Venetian blind model has been proposed, in which the light-reflecting platelets are assumed to be tilted during colour change, resulting in a variation in the spacing between the platelets. In order to quantitatively evaluate the validity of this model, we have performed a detailed optical study of a single stack of platelets inside an iridophore. In particular, we have prepared a new optical system that can simultaneously measure both the spectrum and direction of the reflected light, which are expected to be closely related to each other in the Venetian blind model. The experimental results and detailed analysis are found to quantitatively verify the model.

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Physical methods for investigating structural colours in biological systems

Cited by 163 publications

References 73 publications

Brilliant camouflage : photonic crystals in the diamond weevil, Entimus imperialis

Brilliant camouflage : photonic crystals in the diamond weevil, Entimus imperialis

Polarized iridescence of the multilayered elytra of the Japanese jewel beetle,Chrysochroa fulgidissima

Mechanism of variable structural colour in the neon tetra: quantitative evaluation of the Venetian blind model

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