We investigate the effect on transmission of p-polarized light of the excitation of plasmons of metallic nanocylinders, placed at the exit of subwavelength slits. Morphology-dependent resonaces of the aperture may then be excited, thus leading to supertransmission. The possible enhancement of transmittance is investigated by working out appropriate choices of the geometrical parameters and illumination. Additionally, we study conditions in which supertransmitted light may propagate through sets of metallic cylinders with excited plasmons, in front of either one slit or placed in front of a periodic array of slits. We find that the concentration and intensity of the transmitted field is mainly governed by both the material and geometrical configurations of the particle sets.
The coherent combination of electric and magnetic responses is the basis of the electromagnetic behavior of new engineered metamaterials. The basic constituents of their meta-atoms usually have metallic character and consequently high absorption losses. Based on standard "Mie" scattering theory, we found that there is a wide window in the near-infrared (wavelengths 1 to 3 μm), where light scattering by lossless submicrometer Ge spherical particles is fully described by their induced electric and magnetic dipoles. The interference between electric and magnetic dipolar fields is shown to lead to anisotropic angular distributions of scattered intensity, including zero backward and almost zero forward scattered intensities at specific wavelengths, which until recently was theoretically established only for hypothetically postulated magnetodielectric spheres. Although the scattering cross section at zero backward or forward scattering is exactly the same, radiation pressure forces are a factor of 3 higher in the zero forward condition.
Recently the fundamentals of photonic crystal physics have experienced a revival due to investigations on new structures
possessing properties such as selfwaveguiding and negative refraction. In this communication we present a theory that
gives account of observed total internal reflection beam shifts on the surface of a selfwaveguiding crystal and compare
its analogy and differences with the classical Goos-Hanchen shift. We also investigate the phenomenon of surface wave
resonance excitation in slabs of these arrays as well as those capable of producing images through negative refraction
when cut in a slab shape. A discussion is made of the dispersion relation of these surface waves on comparison with
those of both metals and left handed materials, and its consequences for obtaining superfocusing.
Transmission of light and other electromagnetic waves through apertures smaller than the wavelength are now well
known to yield field intensity enhancements due to morphological resonances of the aperture or, if these are periodically
arranged, as a consequence of Rayleigh or other Wood anomalies. In this communication we study the effect of this
transmission on the photonic force induced by light on a particle in front of a hole practiced in a metallic slab. Several
shapes, constitution and sizes of particles are analyzed. A correlation of the strength of the force with the transmittivity is
found, although it can be either attractive or repulsive depending on the wavelength and the corresponding hole
resonance. Also, we study the effect of coupling of both the hole and the particle Mie resonances.
Following the recent advances in nano-optics, optical manipulation by evanescent fields instead of conventional propagating fields has recently awaken an increasing interest. The main advantages of using low dimensionality fields are (i) the possibility of integrating on a chip applications involving optical forces but also (ii) the absence of limitation by the diffraction limit for the trapping volume. Previous works have investigated theoretically and experimentally the guiding of dielectric and metallic beads at an interface sustaining an extended surface wave. In this work, we study theoretically the radiation forces exerted on Rayleigh dielectric beads under local evanescent illumination. Especially, we consider the configuration where a three-dimensional Gaussian beam is totally reflected at the interface of a glass prism. The results point out the illumination parameters where the gradient forces exceed the scattering force and allow for a stable trapping. The effect of the Goos-Haenchen shift on the location of the trapping site is also discussed.
Due to the fact that the Kirchhoff Approximation (KA) does not involve matrix inversion for solving the forward problem, it is a very useful tool for quickly solving 3D geometries of arbitrary size and shape. Its potential mainly lies in the rapid generation of Green?s functions for arbitrary geometries, which is key to tomography techniques. We here apply it to light diffusion and study its limits of validity, proving that it is a very useful approximation for diffuse optical tomography (DOT). Its use can improve the existing imaging techinques for real time diagnostics in medicine.
In this work we investigate the effect of a layer on Diffuse Optical Tomography of tissue. Such layers could be tissue structures (such as the skin or a fat-layer) or layers formed by compression plates. Our analysis uses an analytical forward model that is based on the angular spectrum representation of the propagating photon density wave in a diffuse medium. The inversion employs a standard perturbation expansion based on the Rytov approximation that is uses appropriate volume segmentation and solved using the algebraic reconstruction technique. The results demonstrate that the effect of biologically relevant multi-layer schemes can lead to significant reconstruction errors both in terms of quantification and positional certainty. The work is focussed on geometries and optical properties typical to the human breast, however the results are general and can apply to other tissue as well.
Recently, it has been shown that clear regions within diffusive media can be accurately modelled within the diffusion approximation by means of a novel boundary condition or by an approximation to it. This can be directly applied to the study of light propagation in brain tissue, in which there exist clear regions, and in particular, the cerebro spinal fluid (CSF) layer under the skull. In this work, we present the effect that roughness in the boundary of non-diffusive regions has on the measured signal, since, in practice, the CSF layer is quite rough. The same conclusions can be extended to any diffusive medium which encloses rough non-diffusive regions. We will demonstrate with numerical calculations that the roughness statistics of the interfaces although not their actual profile must be known a priori in order to correctly predict the shape of the measured signal. We show that as the roughness increases, the effect of the non-diffusive region diminishes until it disappears, thus yielding data similar to those of a fully diffusive region.
Coherent effects associated to the multiple scattering of classical waves in dense media and rough surfaces have been a subject of great interest in the last few years. An important property of the speckle fluctuations is that they generally follow Gaussian first order statistics; namely, the real and imaginary parts of the complex amplitude are Gaussian distributed and uncorrelated, its modulus has a Rayleigh probability density function (PDF), and its intensity follows a negative exponential density distribution. On reflection, very small samples have been shown to produce, both in multiple scattering and in single scattering, speckle fluctuations with non-Gaussian first order statistics.
Reconstruction of astronomical images has been performed by phase retrieval methods from autocorrelation or, equivalently, power spectrum data estimated by applying the stellar speckle interferometry (S.S.I.) technique to photon-limited, turbulence degraded, short exposure images. We present results obtained from real data, and also from computer simulated data. We make comparisons of the results depending both on the phase retrieval method used, and on whether we impose the available information in the object space (autocorrelation), or in the spatial frequency space (power spectrum).
Scattering of electromagnetic waves incident upon randomly rough metal and dielectric surfaces is numerically studied for several dielectric constants e(w) by means of the extinction theorem. A new effect concerning to light transmission through dielectric media is presented. The influence of surface polariton excitation on enhanced backscattering is also analyzed. 1.
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