J. Eur. Opt. Society-Rapid Publ. 22, 12( 2026) 123
The incident light was focused onto a piece of Diptera cuticle at normal incidence using an achromatic 10 objective lens, leading to a beam spot diameter of ca. 30 lm. This lens collected light backscattered by the sample, which was conducted by a beamsplitter through a CP analyser comprising the Fresnel rhomb and a second rotatable polariser. A plane aluminium mirror was used for the measurement calibration.
Supplementary material 3 Figure S2. CP reflectance spectrophotometry was used in order to highlight possible light-polarising effects arising from the pattern observed within Calliphora vicina’ s cuticle that might be associated with a Bouligand structure. Despite the electron micrograph observations, only cross-CP components have significant intensities. Co-CP reflectance spectra that usually contains the signature of Bouligand structures display negligible intensities.
Supplementary material 4 Figure S3. Reflectance spectra of a pseudo-periodic multilayer derived from Calliphora vicina photonic model( Fig. 7) with random thickness deviations of ± 15 nm in the high-contrast layers and ± 5 nm in the low-contrast layers. The resulting calculated spectra were averaged over incidence angles from �5 ° to + 5 °. A broader reflectance peak than the ideal model( Fig. 8a) isobserved, though still narrower than the measured spectrum( Fig. 3a).
Supplementary material 5 CP reflectance was modelled for various incidence angles using a one-dimensional 4 4 matrix method for anisotropic multilayers [ 83 ]. The model comprises a Bouligand structure overlaid by an interferential thin film. The Bouligand structure contained 18 half-pitches of 118 nm, had an average refractive index of 1.56 [ 78 ], and exhibited an in-plane birefringence of 0.018 [ 66 ]. The overlying thin film was modelled as a 180-nm thick isotropic layer with a refractive index of 1.75. All materials were assumed to be non-absorbing.
Supplementary material 6 Figure S4. For comparison, CP reflectance was modelled for a Bouligand structure( 18 half-pitches of 118 nm, an average refractive index of 1.56 [ 78 ], in-plane birefringence of 0.018 [ 66 ]) covered by a 180 nm-thick isotropic film( n = 1.75), calculated for incidence and emergence angles ranging from 0 ° to 75 ° in 15 ° increments in cross-CP configuration( a) and at normal incidence in co- and cross-CP configuration( b). Modelled CP reflectance spectra in( a) appear as broad as the experimental spectra measure from Calliphora vicina( Fig. 3a). The left-left co-CP( LCP-LCP) spectrum exhibits a small peak in the UV range. In the real photonic structure of C. vicina, positional disorder [ 44 ], light absorption, and scattering would likely reduce this co-CP signal to a very weak level.
The supplementary material of this article is available at https:// jeos. edpsciences. org / 10.1051 / jeos / 2025053 / olm.
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