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Spotlight on Optics

Spotlight on Optics


  • April 2011

Optics InfoBase > Spotlight on Optics > Visible light reflection spectra from cuticle layered materials

Visible light reflection spectra from cuticle layered materials

Published in Optical Materials Express, Vol. 1 Issue 1, pp.85-100 (2011)
by Cristian Campos-Fernández, Daniel E. Azofeifa, Marcela Hernández-Jiménez, Adams Ruiz-Ruiz, and William E. Vargas

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Spotlight summary: Sometimes, when asked "What are the applications of Optics?" I get caught off-guard (because the applications of optics are very, very many), and I give a short, generic and conventional answer. I know for a fact that I am not alone in suffering from this "problem," as I have met chemists struggling to give a short, illuminating, and nontechnical answer to the question, "What are the applications of Chemistry?" asked over lunch. I consider, in fact, "Basically everything …" not to be a good answer.

On a less mundane level, I often feel that applications of a science that are as "flexible" and ubiquitous as Optics are limited by the fantasy of the scientists and engineers who are working in the field. When fantasy and knowledge have a good relationship with each other, then wonderful insights and wonderful applications, which are both "off the beaten track" and meaningful and satisfactory, can emerge.

One example is the applications of the science of Optics to the study of insects. In the work of Campos-Fernández et al., light reflection measurements and multilayer reflection calculations are combined to explain the brilliant metallic colors displayed by two species of beetles. The gold and silver colors of, respectively, "Chrysina aurigans" and "Chrysina limbata" can be explained if one admits that the cuticle over the shell of the beetles is organized in a system of chirped layers: the observed colors are "structural" and are not due to pigments. The measurements are very nice and the calculations quite reasonable (and supported by other kinds of measurements published in the literature, such as electron microscope images and data for the refractive indices of the cuticle’s constituents).

Since the authors have identified and pursued a quite unconventional topic for their research, this reviewer, who is not a specialist in the field, tried to exercise his fantasy too and see which possible connections to other research this work stimulates. A brief search on the Internet and a bit of reflection brought forward a couple of possibly relevant thoughts.

One relevant connection is to other works on Optics and insects: I have found recent work in which the possibility that this kind of wasp is able to harvest sunlight energy for its own physiological activity (as far as I know the first observed case in animals) is investigated; among the components of the system that harvests solar energy, there are light-trapping structures in the wasp’s cuticle.

Another idea is imitating nature’s design to produce colored coatings without the use of dyes. It is quite possible to design multilayer, reflective structures without taking inspiration from structures existing in nature, but maybe the solutions that "nature" found can provide insights or show particular effects; again, further consideration of this concept is examined in recent research that also reviews the literature on the organization of beetle shells and their optical properties).

Finally, a question that one could feel compelling is figuring out through which steps evolution produced such relatively complicated and efficient structures: in fact—at least for me—even when a theory or a principle are taken for granted, still the curiosity for the details remains. A parallel thought is whether genetic algorithms are efficient at designing multilayer structures; the Campos-Fernandez research evokes thoughts that for the curious could lead to many interesting reads.

In conclusion, the authors have identified an area of research that promises interesting results and offers an unconventional look on nature. And taking the hint from them could be fruitful.

--Giovanni Piredda

ToC Category: Biomaterials
OCIS Codes: (120.4570) Instrumentation, measurement, and metrology : Optical design of instruments
(160.4670) Materials : Optical materials
(230.4170) Optical devices : Multilayers
(330.1710) Vision, color, and visual optics : Color, measurement
(310.4165) Thin films : Multilayer design

Posted on April 22, 2011

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