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Optical and Structural Characterization of Natural Nanostructures
Linköping University, Department of Physics, Chemistry and Biology, Applied Optics . Linköping University, Faculty of Science & Engineering.
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The spectacular biodiversity of our planet is the result of millions of years of evolution. Over this time animals and plants have evolved and adapted to different environments, developing specific behavioral and physical adaptations to increase their chances of survival. During the last centuries human's curiosity has pushed us to study and understand the phenomena and mechanisms of the nature that surrounds us. This understanding has even led to the fields of biomimetics where we seek solutions to human challenges by emulating nature.

Scarab beetles (from the insect family Scarabaeidae) have fascinated humans for centuries due to the brilliant metallic shine of their chitin-rich exoskeletons and more recently for their ability to polarize reflected light. This doctoral thesis focuses on the optical characterization of the polarized reflected light from beetles in the Chrysina genus, although beetles from other genera also have been investigated. All the Chrysina beetles studied here share one characteristic, they all reflect left-handed near-circular polarized light. In some cases we also detect right-handed polarized light.

We have observed two different main behaviors among the studied Chrysina beetles. Those which are green-colored scatter the reflected polarized light, whereas those with metallic appearance are broadband specular reflectors. We present a detailed analysis of the optical properties with Mueller-matrix spectroscopic ellipsometry combined with optical- and electron-microscopy studies of the exoskeletons. This allow us to create a model that reproduces the optical properties of these structures. The model consists of a chiral (helicoidal) multilayer structure with a gradual change of the pitch and a constant rotation of the optic axis of the layers.

Beetles are not alone to have polarizing structures in nature and it is known that many birds and insects have the ability to detect linearly polarized light. This raises the question of whether the polarization properties of the beetles are the direct or indirect results of evolution or just pure coincidence. In order to get a better understanding of the possible reasons of this particular ability, we present a simulation study of different possible scenarios in nature where incoming light could be polarized or unpolarized, and where we consider detectors (eyes) sensitive to different states of polarized light. If the beetles are able to use this characteristic for camouflage, to confuse predators or for intraspecific communication is,

however, still unknown and requires further investigation.

My research results provide deeper understanding of the properties of light reflected on the beetle's exoskeleton and the nanostructures responsible for the polarization of the reflected light. The developed model could be used as bioinspiration for the fabrication of novel nano-optical devices. My results can also complement biological behavioral experiments aiming to understand the purposes of this specific optical characteristics in nature.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2016. , 53 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1795
National Category
Atom and Molecular Physics and Optics Condensed Matter Physics Biophysics
Identifiers
URN: urn:nbn:se:liu:diva-132613DOI: 10.3384/diss.diva-132613ISBN: 9789176856703 (Print)OAI: oai:DiVA.org:liu-132613DiVA: diva2:1047120
Public defence
2016-12-08, Planck, Fysikhuset, Campus Valla, Linköping, 10:15 (English)
Opponent
Supervisors
Note

The ISBN 978-91-978-91-7685-670-3 in the printed version of the thesis is incorrect. Correct ISBN is 978-91-7685-670-3. The ISBN is corrected in the electronic version.

Available from: 2016-11-16 Created: 2016-11-16 Last updated: 2016-11-16Bibliographically approved
List of papers
1. Polarizing properties and structure of the cuticle of scarab beetles from the Chrysina genus
Open this publication in new window or tab >>Polarizing properties and structure of the cuticle of scarab beetles from the Chrysina genus
2016 (English)In: PHYSICAL REVIEW E, ISSN 2470-0045, Vol. 94, no 1, 012409- p.Article in journal (Refereed) Published
Abstract [en]

The optical properties of several scarab beetles have been previously studied but few attempts have been made to compare beetles in the same genus. To determine whether there is any relation between specimens of the same genus, we have studied and classified seven species from the Chrysina genus. The polarization properties were analyzed with Mueller-matrix spectroscopic ellipsometry and the structural characteristics with optical microscopy and scanning electron microscopy. Most of the Chrysina beetles are green colored or have a metallic look (gold or silver). The results show that the green-colored beetles polarize reflected light mainly at off-specular angles. The gold-colored beetles polarize light left-handed near circular at specular reflection. The structure of the exoskeleton is a stack of layers that form a cusplike structure in the green beetles whereas the layers are parallel to the surface in the case of the gold-colored beetles. The beetle C. gloriosa is green with gold-colored stripes along the elytras and exhibits both types of effects. The results indicate that Chrysina beetles can be classified according to these two major polarization properties.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2016
National Category
Mathematical Analysis
Identifiers
urn:nbn:se:liu:diva-130835 (URN)10.1103/PhysRevE.94.012409 (DOI)000380116500010 ()
External cooperation:
Note

Funding Agencies|Knut and Alice Wallenberg foundation; Swedish Research Council; Centre in Nano Science and Nano Technology (CeNano) at Linkoping University

Available from: 2016-08-26 Created: 2016-08-26 Last updated: 2016-11-16
2. Polarizing properties and structural characteristics of the cuticle of the scarab Beetle Chrysina gloriosa
Open this publication in new window or tab >>Polarizing properties and structural characteristics of the cuticle of the scarab Beetle Chrysina gloriosa
2014 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 571, no 3, 410-415 p.Article in journal (Refereed) Published
Abstract [en]

The scarab beetle Chrysina gloriosa is green with gold-colored stripes along its elytras. The properties of light reflected on these areas are investigated using Mueller-matrix spectroscopic ellipsometry. Both areas reflect light with high degree of left-handed polarization but this effect occurs for specular reflection for the gold-colored areas and for off-specular angles for the green areas. The colors and polarization phenomena originate from reflection of light in the cuticle and a structural analysis is presented to facilitate understanding of the different behaviors of these two areas. Scanning electron microscopy (SEM) images of the cross section of beetle cuticles show a multilayered structure. On the gold-colored areas the layers are parallel to the surface whereas on the green-colored areas they form cusp-like structures. Optical microscopy images show a rather flat surface in the gold-colored areas compared to the green-colored areas which display a net of polygonal cells with star-shaped cavities in the center. Each of the polygons corresponds to one of the cusps observed in the SEM images. Atomic force microscopy images of the star-shaped cavities are also provided. The roughness of the surface and the cusp-like structure of the green-colored areas are considered to cause scattering on this area.

Place, publisher, year, edition, pages
Elsevier, 2014
Keyword
Scarab beetle; Near-circular polarization; Mueller-matrix spectroscopic ellipsometry
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:liu:diva-112885 (URN)10.1016/j.tsf.2013.11.149 (DOI)000346055200013 ()
Conference
ICSE-VI International Conference on Spectroscopic Ellipsometry May 2013
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation
Available from: 2014-12-18 Created: 2014-12-18 Last updated: 2016-11-16Bibliographically approved
3. Polarization of light reflected from Chrysina gloriosa under various illuminations
Open this publication in new window or tab >>Polarization of light reflected from Chrysina gloriosa under various illuminations
2014 (English)In: Materials Today: Proceedings, Elsevier Ltd , 2014, Vol. 1, 172-176 p.Conference paper (Refereed)
Abstract [en]

When illuminated with unpolarized light, the scarab beetle Chrysina gloriosa, reflects left-handed near-circularly polarized light for a broad range of angles of incidence and wavelengths in the visible. It is, however, known that light scattered from the sky, reflected on water or transmitted through leaves often is linearly polarized. In this study we have analysed the polarization of light reflected on this beetle when illuminated with different polarization states of light. We have also analysed how the response would be with a polarization-sensitive detector. The reflected irradiance is shown to be highest when the incident light is s-polarized or left-handed polarized and the detector is unpolarized (or vice versa). In the case in which both, the source and the detector, are polarized, the irradiance is highest when both are s-polarized. On the contrary the visibility is low when the source is s-polarized and the detector is p-polarized.

Place, publisher, year, edition, pages
Elsevier Ltd, 2014
Series
, Materials Today: Proceedings, ISSN 2214-7853
Keyword
Mueller-matrix spectroscopic ellipsometry; Near-circular polarization; Scarab beetle
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-116444 (URN)10.1016/j.matpr.2014.09.020 (DOI)2-s2.0-84923048023 (ScopusID)
Conference
Living Light: Uniting biology and photonics - A memorial meeting in honour of Prof Jean-Pol Vigneron
Available from: 2015-03-27 Created: 2015-03-26 Last updated: 2016-11-16
4. Comparison and analysis of Mueller-matrix spectra from exoskeletons of blue, green and red Cetonia aurata
Open this publication in new window or tab >>Comparison and analysis of Mueller-matrix spectra from exoskeletons of blue, green and red Cetonia aurata
2014 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 571, 739-743 p.Article in journal (Refereed) Published
Abstract [en]

The exoskeleton, also called the cuticle, of specimens of the scarab beetle Cetonia aurata is a narrow-band reflector which exhibits metallic shine. Most specimens of C. aurata have a reflectance maximum in the green part of the spectrum but variations from blue–green to red–green are also found. A few specimens are also more distinct blue or red. Furthermore, the reflected light is highly polarized and at near-normal incidence near-circular left-handed polarization is observed. The polarization and color phenomena are caused by a nanostructure in the cuticle. This nanostructure can be modeled as a multilayered twisted biaxial layer from which reflection properties can be calculated. Specifically we calculate the cuticle Mueller matrix which then is fitted to Mueller matrices determined by dual-rotating compensator ellipsometry in the spectral range 400–800 nm at multiple angles of incidence. This non-linear regression analysis provides structural parameters like pitch of the chiral structure as well as layer refractive index data for the different layers in the cuticle. The objective here is to compare spectra measured on C. aurata with different colors and develop a generic structural model. Generally the degree of polarization is large in the spectral region corresponding to the color of the cuticle which for the blue specimen is 400–600 nm whereas for the red specimen it is 530–730 nm. In these spectral ranges, the Mueller-matrix element m41 is non-zero and negative, in particular for small angles of incidence, implicating that the reflected light becomes near-circularly polarizedwith an ellipticity angle in the range 20°–45°.

Place, publisher, year, edition, pages
Elsevier, 2014
Keyword
Mueller-matrix ellipsometry; Scarab beetles; Chiral structures; Circular polarization; Natural photonic structures
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-112685 (URN)10.1016/j.tsf.2014.02.012 (DOI)000346055200076 ()
Conference
6th International Conference on Spectroscopic Ellipsometry (ICSE-VI), May 26–31, 2013, Kyoto, Japan
Funder
Knut and Alice Wallenberg FoundationSwedish Research Council
Available from: 2014-12-08 Created: 2014-12-08 Last updated: 2016-11-16Bibliographically approved

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