This PDF file contains the front matter associated with SPIE Proceedings Volume 8480 including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.
Two-dimensional fibrous photonic structures are frequent in nature. Such structures come in at least three different classes: fibre bundles, cylindrical multilayers and longitudinal patterning. We propose reviewing the occurrence of fibrous photonic structures in nature and develop the physical arguments that explain the optical properties of these light-reflecting fibers, isolated or grouped in more or less dense assemblies. We will also indicate how multiscale models appropriate for those kind of structures can be approached. With appropriate adaption of the size of the structure, the arguments are applicable in the visible, near-ultraviolet, infrared radiations, and in the thermal (far infrared) regime.
Structurally colored nano-architectures found in living organisms are complex optical materials, giving rise to multiscale visual effects. In arthropods, these structures often consist of porous biopolymers and form natural photonic crystals. A signature of the structural origin of coloration in insects is iridescence, i.e., color changes with the viewing angle. In the scales located on the elytra of the Brazilian weevil Entimus imperialis (Curculionidae), three-dimensional photonic crystals are observed. On one hand, each of them interacts independently with light, producing a single color which is observed by optical microscopy and ranges from blue to orange. On the other hand, the color perceived by the naked eye is due to multi-length-scale light effects involving different orientations of a single photonic crystal. This disorder in crystal orientations alters the light propagation in such a way that the crystal iridescence is removed. Entimus imperialis is therefore a remarkable example of additive photonic colors produced by a complex multi-scale organic architecture. In order to study this specific natural photonic structure, electron microscopy is used. The structure turns out to be formed of a single type of photonic crystal with different orientations within each scale on the elytra. Our modeling approach takes into account the disorder in the photonic crystals and explains why the structure displays bright colors at the level of individual scales and a non-iridescent green color in the far-field.
Fluorescent molecules are much in demand for biosensors, solar cells, LEDs and VCSEL diodes, therefore, considerable efforts have been expended in designing and tailoring fluorescence to specific technical applications. However, naturally occurring fluorescence of diverse types has been reported from a wide array of living organisms: most famously, the jellyfish Aequorea victoria, but also in over 100 species of coral and in the cuticle of scorpions, where it is the rule, rather than the exception.
Despite the plethora of known insect species, comparatively few quantitative studies have been made of insect fluorescence. Because of the potential applications of natural fluorescence, studies in this field have relevance to both physics and biology. Therefore, in this paper, we review the literature on insect fluorescence, before documenting its occurrence in the longhorn beetles Sternotomis virescens, Sternotomis variabilis var. semi rufescens, Anoplophora elegans and Stellognatha maculata, the tiger beetles Cicindela maritima and Cicindela germanica and the weevil Pachyrrhynchus gemmatus purpureus. Optical features of insect fluorescence, including emitted wavelength, molecular ageing and naturally occurring combinations of fluorescence with bioluminescence and colour-producing structures are discussed.
It is known that the structural colors of some beetles originate from multilayer thin-film interference. We
investigated such an example, a jewel beetle Chrysochroa fulgidissima, to quantitatively characterize the coloration mechanisms. The essential physical factors of the iridescence were elucidated by careful determinations of the structural parameters, measurements of angle and polarization-dependent reflection spectra, and theoretical modeling of the multilayer system. On the basis of the elucidated coloration mechanisms, we successfully prepared a dielectric thin film structure that reproduces the iridescence of the jewel beetle.
We discuss the deflection of light and Shapiro delay under the influence of gravity as described by Schwarzschild metric. We obtain an exact expression based on the coordinate velocity, as first set forth by Einstein, and present a discussion on the effect of velocity anisotropy. We conclude that the anisotropy in the coordinate velocity, as the velocity apparent to a distant observer, gives rise to a third order error in the deflection angle, so that the practical astronomical observations from gravitational lensing data remain inconclusive on the anisotropy. However, measurement of Shapiro delay provides a fairly convenient way to determine whether the spacetime is optically anisotropic for a distant observer or not. We calculate the Shapiro delay for a round trip path between Earth and Venus and observe excellent agreement to two experimentally reported values measured during a time span of six months in 1967, without any need to extra fitting parameters. This is while the expected delay obtained from an isotropic light velocity as described by Einstein's model suffers from much larger errors under similar conditions. This article illustrates the usefulness of the equivalent medium theory in understanding of general theory of relativity.
Proc. SPIE 8480, Observation of spatial polarization structure near unfolding point of an optical vortex beam using a birefringent Mach-Zehnder interferometer, 848008 (11 October 2012); doi: 10.1117/12.930564
A uniformly polarized optical vortex (OV) entering a birefringent crystal is known to unfold into complex polarization structures due to the separation of ordinary and extraordinary rays. The interplay between the topological structures in scalar and vector optics has been studied at the output of finite-length crystals. But the polarization transformation near the unfolding point where the beam initially enters the crystal has not been observed so far. In this paper, we experimentally investigate the spatial polarization structure very near the unfolding point of a uniformly polarized OV beam propagating in a birefringent crystal by constructing a birefringent interferometer. The unfolding point is reconstructed by folding back the two separated beams into a single beam using another identical birefringent crystal, resulting in a birefringent interferometer of Mach-Zehnder type. Small rotation of the second crystal produces output beams with varying separation near the unfolding point. The spatial polarization structure of the output beam is investigated by measuring the Stokes parameters. Such understanding of the connection between defects of scalar optics and vector optics through birefringence will help to shape the spatial polarization states of laser beams for various spectroscopic and microscopic applications.
We have discovered a variety of types of optical evidence that demonstrate artists as early as Jan van Eyck and
Robert Campin (c1425) used optical projections as aids for producing certain elements in their paintings. We also
found optical evidence within works by well-known later artists, including Bermejo (c1475), Lotto (c1525),
Caravaggio (c1600), de la Tour (c1650), Chardin (c1750) and Ingres (c1825), showing that the use of optical
projections by artists continued up to the development of photography and beyond. However, it is important to
emphasize this does not mean that paintings are effectively photographs. The mind as well as the hand of the artist
is intimately involved in the creation process, so these complex images are much more than simply traced images
that have been projected.
Underwater, in littoral zones, natural illumination typically varies strongly temporally and spatially. Waves on the water surface refract light into the water in spatiotemporal varying intensity. The resulting underwater illumination field forms a caustic network and is known as flicker. Studies in underwater computer vision typically consider flicker to be an undesired effect. In contrast, recent studies1-3 show that the spatiotemporally varying caustic network can be useful for stereoscopic vision, naturally leading to range mapping of the scene. In this paper, we survey these studies.
Range triangulation by stereoscopic vision requires the determination of correspondence between image points in different viewpoints. This is typically a difficult problem. However, the spatiotemporal caustic pattern effectively encodes stereo correspondences. Thus, the use of this effect is termed2CauStereo. The temporal radiance variations due to flicker are unique to each object point. Thus, correspondence of image points per object point becomes unambiguous. A variational optimization formulation is used in practice to find the dense stereo correspondence field. This formulation helps overcome uncertain regions (e.g., due to shadows) and shortens the acquisition time. Limitations of the approach are revealed by ray-tracing simulations. The method was demonstrated by underwater field experiments.2
Fireflies lighten up our warm summer evenings. There is more physic behind these little animals than anyone of us could imagine. In this paper we analyze from a physical point of view one structure found on the firefly lantern, the one which best improves light extraction. Moreover, simulations will be done to show why this specific structure may be more effective than a ”human-thought” one.
Scales from specific weevils, longhorns and butterflies have been shown to internally contain a photonic structure that can be described as the agglomeration of photonic crystallites. Usually, the same local photonic structure is found in all crystallites, with different orientations. This distribution is investigated by analysing a large amount of fractured scales. The visual effects produced by fractioning the photonic-crystal into the aggregation of reoriented photonic crystallites can be, for increasing disorder, (1) the loss of iridescence and the loss of metallicity for diffuse coloration, (2) the loss of coloration.