Experimental observation of rainbow scattering by a coated cylinder: twin primary rainbows and thin-film interference

We experimentally examine the primary rainbow created by the illumination of a coated cylinder. We present a simple technique for varying the coating thickness over a wide range of values, and we see evidence for two different scattering regimes. In one, where the coating thickness is large, twin rainbows are produced. In the second, where the coating is thin enough to act as a thin film, a single rainbow is produced whose intensity varies periodically as the coating thickness varies. We find good agreement with previous theoretical predictions.     

Theory of total-internal-reflection tomography

A method is presented to reconstruct three-dimensional tomographic images of weakly scattering objects with subwavelength resolution. The method may be applied to data available in phase-sensitive, total-internal-reflection microscopy. The results follow from an analysis of the near-field inverse scattering problem with evanescent waves.     

Visibility of natural tertiary rainbows

Naturally occurring tertiary rainbows are extraordinarily rare and only a handful of reliable sightings and photographs have been published. Indeed, tertiaries are sometimes assumed to be inherently invisible because of sun glare and strong forward scattering by raindrops. To analyze the natural tertiary's visibility, we use Lorenz-Mie theory, the Debye series, and a modified geometrical optics model (including both interference and nonspherical drops) to calculate the tertiary's (1) chromaticity gamuts, (2) luminance contrasts, and (3) color contrasts as seen against dark cloud backgrounds. Results from each model show that natural tertiaries are just visible for some unusual combinations of lighting conditions and raindrop size distributions.     

Simulating rainbows and halos in color

Geometric optics rainbows and ice-crystal halos that include some effects of a Rayleigh-scattering atmosphere and a cloud of finite optical thickness are simulated in color by the use of a Monte Carlo approach.     

Confocal total-internal-reflection fluorescence microscopy with a high-aperture parabolic mirror lens

We present a theoretical study of a new total-internal-reflection fluorescence microscope for the detection of fluorescence at a water-glass interface. The system is designed for confocal imaging and spectroscopy of nanoparticles and single molecules. Focusing and fluorescence collection through standard glass coverslips is accomplished by a parabolic mirror lens. The large aperture of the element is used to excite fluorescence within the evanescent field of a diffraction-limited focus and to collect focal emission with high efficiency. Tight focusing and supercritical excitation reduce the detection volume for fluorescent analyte molecules well below that of an attoliter (10(-18) L), which can be advantageous for monitoring surface binding of single molecules without interference from fluorescence of the unbound bulk. Calculations of the electric fields in the focus region and simulated confocal imaging demonstrate the performance of the system.     

Irradiance formations of on-axis Lambertian pointlike sources in polygonal total-internal-reflection straight light pipes

Different geometric shapes of light pipes cause different irradiance distributions. We analytically explore the irradiance distributions of on-axis Lambertian pointlike sources in polygonal total-internal-reflection (TIR) straight light pipes. It is analytically shown that the irradiance of pentagonal light pipes concentrates on the center of the exit plane. Numerical verifications are also provided, and experimental explorations with different shapes of acrylic light pipes are carried out for comparison. We also analyze the influence of light-pipe length on distribution uniformity and deduce the smallest uniform-mixing length/circumradius ratios for polygonal light pipes.     

Fast analysis method for polarization-dependent performance of a concave diffraction grating with total-internal-reflection facets

A fast simulation method for a waveguide-based concave grating with total-internal-reflection (TIR) facets is presented using the Kirchhoff-Huygens principle. Unlike the conventional scalar method, modifications are made to take into account the influence of the Goos-H?nchen (GH) shift. The simple method is in good agreement with a numerical method based on rigorous coupled-wave analysis for a wide range of practical device parameters and can provide an insightful physical explanation for the numerical results. It is shown that the GH shift is a main contributing factor for the loss and the polarization-dependent loss of an etched diffraction grating demultiplexer with TIR facets.     

Amplification of high-order rainbows of a cylinder with an elliptical cross section

The intensity of high-order rainbows for normally incident light and certain rotation angles of a cylinder with an elliptical cross section is greatly amplified with respect to the intensity for a circular cross-sectional cylinder. The amplification is due to a number of the internal reflections occurring past the critical angle for total internal reflection, and the effect is especially strong for odd-order rainbows, beginning with the third order. Experimentally, the fourth- and the fifth-order rainbows of a nearly elliptical cross-sectional glass rod were observed and analyzed.     

Simulation of rainbows,coronas, and glories by use of Mie theory

Mie theory offers an exact solution to the problem of scattering of sunlight by spherical drops of water. Until recently, most applications of Mie theory to scattering of light were restricted to a single wavelength. Mie theory can now be used on modern personal computers to produce full-color simulations of atmospheric optical effects, such as rainbows, coronas, and glories. Comparison of such simulations with observations of natural glories and cloudbows is encouraging.     

Experimental observation of internal water curing of concrete

Internal water curing has a significant effect on concrete. In addition to affecting hydration and moisture distribution, it influences most concrete properties, such as strength, shrinkage, cracking, and durability. The following paper is an overview of experimental methods to study internal water curing of concrete and its consequences. The special techniques needed to study internal water curing are dealt with along with the consequences of this process. Examples of applications are given and new measuring techniques that may potentially be applied to this field are addressed.     

Supernumerary spacing of rainbows produced by an elliptical-cross-section cylinder. I. Theory

A sequence of rainbows is produced in light scattering by a particle of high symmetry in the short-wavelength limit, and a supernumerary interference pattern occurs to one side of each rainbow. Using both a ray-tracing procedure and the Debye-series decomposition of first-order perturbation wave theory, I examine the spacing of the supernumerary maxima and minima as a function of the cylinder rotation angle when an elliptical-cross-section cylinder is normally illuminated by a plane wave. I find that the supernumerary spacing depends sensitively on the cylinder-cross-section shape, and the spacing varies sinusoidally as a function of the cylinder rotation angle for small cylinder ellipticity. I also find that relatively large uncertainties in the supernumerary spacing affect the rainbow angle only minimally.     

Experimental observation of fracture patterns in layered slate

The layered structure of slate rock induces strength anisotropy. The strength in the direction of the layers (schistosity) is considerably smaller than in any other direction. A series of loading tests on circular samples and another series of loading tests on rectangular samples are performed to examine fracture patterns in slate. The tests are monitored by visual recordings and by recording acoustic emission. The processing of this data results in localization. This allows identification and analysis of the occurrence and propagation of the individual fractures. It is shown that the strength anisotropy on μ-scale is the key factor behind the strength anisotropy on sample scale, as well as behind the deformation behaviour of the sample. In addition, it is observed that a small variability in the layer direction can affect the fracture pattern considerably.     

Analysis and design of a concave diffraction grating with total-internal-reflection facets by a hybrid diffraction method

A novel hybrid diffraction method is introduced to simulate the diffraction and imaging of a planar-integrated concave grating that has total internal reflection (TIR) facets. The Kirchhoff-Huygens diffraction formula is adopted to simulate the propagation of the lightwave field in the free-propagation region, and a rigorous coupled-wave analysis is used to calculate the polarization-dependent diffraction by the grating. The hybrid diffraction method can be used to analyze accurately the imaging properties as well as the polarization-dependent diffraction characteristics of a concave grating. The dependence of several merit parameters of a concave grating with TIR facets on its basic geometric parameters is studied. Compared with one with metallic echelle facets, a concave grating with TIR facets shows a much lower polarization-dependent loss. Since more performance specifications can be considered in the design of a concave grating than with the conventional scalar method, design error can be reduced greatly with the present hybrid diffraction method.     

Exuberant interference: rainbows,tides, edges, (de)coherence..

Young's pioneering studies of interference have led to fundamental developments in wave physics. Supernumerary rainbows were the first example of diffraction associated with caustics. Cotidal lines (connecting places where the tide is high at a given time) were the first example of wavefronts in the modern sense (pattern of phase contours (arg psi(1) + psi(2)) of the superposition of waves psi(1) and psi(2), rather than the superposed patterns of the separate phases arg psi(1) and arg psi(2)), and led to the discovery of phase singularities. Edge-diffracted waves extend the range of asymptotic methods applied to waves and continue to find diverse and unexpected applications. Young's understanding of the conditions for observing interference are now part of decoherence theory, which explains, for example, the emergence of the classical world from the quantum world.     

Experimental observation of laser-induced modification of Mössbauer spectra

Abstract

The modification of Fe⁵⁷ Mössbauer spectra of a MgO single crystal under the action of laser radiation was observed. A possible interpretation of the observed effect is proposed.     

Imaging polarimetry of the fogbow: polarization characteristics of white rainbows measured in the high Arctic

The knowledge on the optics of fogbows is scarce, and their polarization characteristics have never been measured to our knowledge. To fill this gap we measured the polarization features of 16 fogbows during the Beringia 2005 Arctic polar research expedition by imaging polarimetry in the red, green and blue spectral ranges. We present here the first polarization patterns of the fogbow. In the patterns of the degree of linear polarization p, fogbows and their supernumerary bows are best visible in the red spectral range due to the least dilution of fogbow light by light scattered in air. In the patterns of the angle of polarization α fogbows are practically not discernible because their α-pattern is the same as that of the sky: the direction of polarization is perpendicular to the plane of scattering and is parallel to the arc of the bow, independently of the wavelength. Fogbows and their supernumeraries were best seen in the patterns of the polarized radiance. In these patterns the angular distance δ between the peaks of the primary and the first supernumerary and the angular width σ of the primary bow were determined along different radii from the center of the bow. δ ranged between 6.08° and 13.41°, while σ changed from 5.25° to 19.47°. Certain fogbows were relatively homogeneous, meaning small variations of δ and σ along their bows. Other fogbows were heterogeneous, possessing quite variable δ- and σ-values along their bows. This variability could be a consequence of the characteristics of the high Arctic with open waters within the ice shield resulting in the spatiotemporal change of the droplet size within the fog.     

Experimental observation of plastic deformation areas, using an acoustic microscope

Novel techniques are described for the observation of plastic deformation areas by using an acoustic microscope. On a test piece subjected to plastic deformation, an area was found that had an abnormal contrast in the crystal grain and a pointed end at the V notch. Calculation of the propagation velocity of the surface acoustic wave (SAW) showed a difference of several percent between this area and the rest of the test piece. It has been presumed that this difference reflects the local plastic deformation, and that the abnormal contrast area corresponds to the image of the two-dimensionally distributed plastic deformation area of metals.     

Experimental observation of self-transparency in an epoxybased polymer dispersed liquid crystal

Abstract

We report the observation of a self-switching effect from an opaque to a transparent state occurring at a critical incident intensity in a polymer dispersed liquid crystal. This self-transparency effect is analysed taking into account the beam profile variations of the light propagating inside such a medium. A clear self-confinement of the laser beam travelling in this composite material is also presented.