Non-diffracting light in nature: Anomalously reflected self-healing Bessel beams from jewel scarabs

Petr Bouchal,Martin Konečný,Josef Kapitán,Marek Zbončák,Zdeněk Bouchal

doi:10.1063/1.5125045

Petr Bouchal, Martin Konečný + Show 3 more

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https://doi.org/10.1063/1.5125045

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Abstract

We report a study of spatial light modulation in the photonic structure of jewel scarabs, revealing the interplay of the polarization and phase control of light, which is not possible with the current optical technology. Phase measurements performed on jewel scarabs demonstrate that the polarization anomalous (helicity-preserving) reflection of light occurs together with alteration of the dynamic phase associated with the optical path length. This control of light differs from the operation of artificially prepared polarization-sensitive structures, shaping light through the geometric phase altered by the polarization transformation. Challenging three-dimensional imaging of the cuticle, requiring high-resolution quantitative mapping of steep phase changes, has been achieved owing to the optical performance of recently developed geometric-phase microscopy. We find that the cuticle of jewel scarabs is formed of micrometer-sized axicon cells, generating thousands of Bessel beams with subwavelength spot size. The nondiffracting features and the self-healing ability of the Bessel beams originating from the beetle Chrysina gloriosa are demonstrated experimentally. Considering Bragg reflection and shaping of RGB components of white light Bessel beams, we explain the spatial structuring of colors in microscopic images of jewel scarabs and reveal the conversion of colors when changing the distance from the cuticle. The functionality and performance of the cuticle axicon cells are discussed in comparison with high-aperture dielectric meta-axicons, and potential applications in colorimetric refractive index sensing are outlined.

Highlights

An exceptional diversity of natural phenomena, including high reflectivity or transmissivity, polarization selectivity, dichroism, iridescence, or structural color, is achieved through the interaction of light with photonic structures of great morphological variability.1,2 In the insect kingdom, iridescent beetles that preferentially reflect light with left-handed circular polarization (LHCP) have garnered much interest.3,4 The cuticles of these beetles comprise clusters of chitin microfibrils capable of self-organization into a helicoidal Bouligand structure,5,6 with properties similar to the cholesteric liquid crystal phase.7,8 In this structure, the microfibrils are aligned parallel in a plane, and the orientation between adjacent planes is slightly twisted
The spatially structured cells forming the cuticle have been shown to be micrometer-sized reflective axicons that generate nondiffracting Bessel beams. These cuticle biomodulators provide remarkable optical performance, competitive with the high-aperture meta-axicons recently designed for generating subwavelength Bessel beams
The dielectric meta-axicon is formed by regularly spaced TiO2 nanofins acting as a half-wave plate reversing the handedness of the circular polarization of the incident light

Summary

Introduction

An exceptional diversity of natural phenomena, including high reflectivity or transmissivity, polarization selectivity, dichroism, iridescence, or structural color, is achieved through the interaction of light with photonic structures of great morphological variability. In the insect kingdom, iridescent beetles that preferentially reflect light with left-handed circular polarization (LHCP) have garnered much interest. The cuticles of these beetles comprise clusters of chitin microfibrils capable of self-organization into a helicoidal Bouligand structure, with properties similar to the cholesteric liquid crystal phase. In this structure, the microfibrils are aligned parallel in a plane, and the orientation between adjacent planes is slightly twisted. An exceptional diversity of natural phenomena, including high reflectivity or transmissivity, polarization selectivity, dichroism, iridescence, or structural color, is achieved through the interaction of light with photonic structures of great morphological variability.. Iridescent beetles that preferentially reflect light with left-handed circular polarization (LHCP) have garnered much interest.. Iridescent beetles that preferentially reflect light with left-handed circular polarization (LHCP) have garnered much interest.3,4 The cuticles of these beetles comprise clusters of chitin microfibrils capable of self-organization into a helicoidal Bouligand structure, with properties similar to the cholesteric liquid crystal phase.. The cuticles of these beetles comprise clusters of chitin microfibrils capable of self-organization into a helicoidal Bouligand structure, with properties similar to the cholesteric liquid crystal phase.7,8 In this structure, the microfibrils are aligned parallel in a plane, and the orientation between adjacent planes is slightly twisted. Light with LHCP is selectively reflected within the spectral bandwidth given by the birefringence and the pitch of the structure, and broadband reflection may take place when the pitch varies across the cuticle. The anomalous reflection of light has been widely examined in relation to animal behavior and as part of an extensive study of photonics in nature. Structural coloration, arising as a result of Bragg reflection from helicoidally stacked cellulose microfibrils that form layers in the cell walls of the epicarp, has been examined in plants.

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