J. M. Saiz

Light scattering resonances in small particles with electric and magnetic properties

Lorenz-Mie resonances produced by small spheres are analyzed as a function of their size and optical properties (epsi > or < 0, mu > or < 0). New generalized (mu not equal to 1) approximate and compact expressions of the first four Lorenz-Mie coefficients (a1, b1, a2, and b2) are calculated. With these expressions and for small particles with various values of epsi and mu, the extinction cross section (Q(ext)) is calculated and analyzed, in particular for resonant conditions. The dependence on particle size of the extinction resonance, together with the resonance shape (FWHM), is also analyzed. In addition to the former analysis, a study of the scattering diagrams for some interesting values of epsi and mu is also presented.

Directionality in scattering by nanoparticles: Kerker's null-scattering conditions revisited.

Since the first studies made by Kerker in the 1970s stating the conditions for null light scattering in certain directions by particles, such conditions have remained unquestioned. The increasing interest in scattering directionality by tuning the optical properties of materials demands a new analysis of this problem. In addition, as has been shown recently, one of Kerkers statements does not comply with the optical theorem. We propose corrected expressions for the null-scattering conditions that satisfy the optical theorem.

Plasmon spectroscopy of metallic nanoparticles above flat dielectric substrates.

We numerically analyze the spectral properties of localized plasmon resonances in metal nanoparticles when these are above a dielectric substrate. This analysis is performed as a function of the various parameters involved in the problem (relative optical properties, particle-substrate separation, angle of incidence, etc.). It can be shown that from the spectral behavior of the resonance in the far field, information about particle near-field interactions can be obtained.

Sizing particles on substrates. A general method for oblique incidence

We have developed an experimental light-scattering method to size metallic spherical and cylindrical particles on flat substrates using obliquely incident light. We modify an earlier model to include effects such as the shadowing of the incident and scattered beams. We provide empirical expressions for sizing spheres and cylinders on substrates based on the positions of their minima. The results have been experimentally verified for both types of particle. The extension of the method to oblique incidence angles allows an alternative dynamic procedure.

Experimental study of copolarized light scattering by spherical metallic particles on conducting flat substrates

We present light-scattering experiments for well-characterized random conducting surfaces composed of spherical particles on flat substrates. The experiments were carried out for both sparse (low particle-surface density) and dense targets by using particle sizes of the order of the incident wavelength (λ = 0.633 μm). We analyzed both small incidence angles and grazing incidence and present the results for both p and s polarizations. Also, we present the results of computer-simulated light-scattering experiments based on the extinction theorem for a one-dimensional, perfectly conducting surface model for comparison with the experimental results. This model is composed of an array of parallel cylinders upon a flat substrate whose separations follow an exponential distribution corresponding to a pure Poisson process. The possible relevance of these results to radar scattering from the sea surface is also briefly discussed.

Surface inspection by monitoring spectral shifts of localized plasmon resonances

We present a numerical study of the spectral variations of localized surface plasmon resonances (LSPR) in a 3D-probe metallic nanoparticle scanned over an inhomoegeneous dielectric surface. The possibilities for both, index monitoring and lateral resolution at nanoscale level are explored, with special attention paid to the shape of the probe and the profile of the near field underneath.

SCATTERING BY A METALLIC CYLINDER ON A SUBSTRATE : BURYING EFFECTS

Experimental measurements of the light scattered from a metallic circular cylinder, with a section diameter comparable with the incident wavelength, upon a metallic flat substrate are presented. The validity of the theoretical numerical calculation obtained from a one-dimensional model based on Maxwells coupled integral equations for real metals is demonstrated by comparison with the experimental results. The theoretical model is able to reproduce a geometric feature as the partial burying of the cylinder in the substrate because of the sputtering process.

METALLIC PARTICLE SIZING ON FLAT SURFACES : APPLICATION TO CONDUCTING SUBSTRATES

A fast and accurate microsizing method is introduced and analyzed for metallic protuberances on flat substrates. It is based on the measurement of the minima angular positions of the S‐polarized far field scattering patterns at normal incidence. The proposed method has been theoretically and experimentally checked for both cylindrical and spherical metallic protuberances on conducting flat substrates. The excellent agreement between theory and experiment proves the efficiency of the method. We also comment on the application of this method for other protuberance geometries and different substrates other than metallic.

Backscattering from particulate surfaces: experiment and theoretical modeling

The copolarized backscattered intensity from surfaces composed of metallic particles on conducting flat substrates is analyzed experimentally as a function of the incidence angle. The analysis is done for particle sizes smaller than, comparable to, and larger than the incident wavelength (0.633 μm) and for low particle surface densities. Numerical calculations based on the extinction theorem for a onedimensional surface model consisting of an infinitely long cylinder located on a flat substrate for the same optical constants used in the experiment are also presented for qualitative comparison with the experimental results. This serves to analyze the effect of particle aggregation. For the surfaces with particles smaller than the incident wavelength, conclusions are drawn concerning the possible relevance of this study in radar wave scattering from the sea surface.

Exception for the zero-forward-scattering theory

Studies on single scattering of electromagnetic waves by magnetic particles were reported in the 1980s by Kerker et al. [J. Opt. Soc. Am.73, 765 (1983)]. They obtained that very small spherical particles with electric permittivity and magnetic permeability values such that epsilon=(4-mu)/(2mu+1) do not produce forward scattering. We show here that this condition contains an interesting exception at (epsilon=-2, mu=-2) when electric and magnetic resonances are present and around which the scattered field distribution is computed and described showing a polarization-insensitive behavior at the point (epsilon=-2, mu=-2).