Electromagnetic scattering by an aggregate of spheres: errata

Critical assessment of enhancement factor measurements in surface-enhanced Raman scattering on different substrates

The SERS enhancement factor (SERS-EF) is one of the most important parameters that characterizes the ability of a given substrate to enhance the Raman signal for SERS applications. The comparison between dynamic and static substrates, however, should not be performed in sense of SERS-EF.

Shaping emission spectra of fluorescent molecules with single plasmonic nanoresonators

We show that plasmonic nanoresonators composed of two gold nanoparticles change not only the intensity but also the spectral shape of the emission of fluorescent molecules. The plasmonic resonance frequency can be tuned by varying the distance between the nanoparticles, which allows us to selectively favor transitions of a fluorescent molecule to a specific vibrational ground state. Experimental data from correlated scattering and fluorescence microscopy agree well with calculations in the framework of generalized Mie theory. Our results show that the widely used description of a dye molecule near a metal surface as a mere two-level system is inadequate.

Radiative scattering properties of an ensemble of variously shaped small particles

This paper presents a rigorous solution to the scattering of a monochromatic plane wave by an arbitrary configuration of wavelength-sized small particles that can be of different shape, structure, size, and composition. A T-matrix formulation is developed for the calculation of optical cross sections and the asymmetry parameter of such an ensemble of scatterers in both fixed and random orientations. The solution is based on the T matrix T(jl), that is, the inverse of the coefficient matrix of boundary condition equations. A linear system containing T(jl) is derived to efficiently solve the T matrix, which is required in the practical implementation of the solution.

Apertureless near-field optical microscopy of metallic nanoparticles

Image formation in apertureless near-field optical microscopes employing evanescent-wave excitation is studied quantitatively as a function of the polarisation and the wavelength of the excitation. Aggregate Mie theory is used to describe the probe-sample interactions self-consistently, including retardation. Only p-polarised excitation yields images, which closely reproduce the sample, and the contrast is much higher in this case than for s-polarised waves. Particular attention is paid to the case of imaging of metallic nanoparticles, for which local and nonlocal versions of aggregate Mie theory are compared. Nonlocality arises from the excitation of longitudinal bulk plasmons at the particle surface. It is shown that this effect is essential in the imaging of such particles and implies comparatively rapid convergence, in contrast to the local theory. The converged images calculated within the nonlocal theory resemble the results of the local theory, when, arbitrarily, within the latter only dipole-dipole interactions are taken into account. Significant qualitative and quantitative differences, however, are shown to exist. Signal and contrast enhancements due to resonant excitation of surface plasmon polaritons are studied quantitatively using the results of the converged nonlocal theory.

Electric field autocorrelation functions for beginning multiple rayleigh scattering

The polarization-resolved electric field autocorrelation function for p-order scattering was derived from the order-of-scattering solution of the exact equations for electromagnetic multiple Rayleigh scattering and was calculated for 2 </= p </= 6 for particles undergoing diffusive motion in an idealized sample cell. It was found that the polarization-channel and the scattering-angle dependence of the p-order autocorrelation function approximately decoupled from the delay-time dependence for p ? 3. The polarization-channel and the scattering-angle dependence were analytically calculated, and the delay-time dependence was analytically approximated. The resulting analytical model for the polarization-resolved autocorrelation function for beginning multiple Rayleigh scattering was then tested against experimental autocorrelation data. The data were found to be well fitted by the model.

Calculation of the heat-source function in photophoresis of aggregated spheres

We present theoretical results for the source function in photophoresis of an arbitrary aggregate of spheres that are homogeneous and isotropic piecewise. This source function directly represents the distribution of electric fields inside the spheres. Our calculation is based on a rigorous analytic solution to the radiative multisphere-scattering problem developed recently [Y.-l. Xu, Appl. Opt. 34, 4573 (1995); 36, 9496 (1997); Phys. Lett. A 249, 30 (1998)]. When an aggregate degenerates to a single sphere, the results are exactly the same as those given by the Mie theory. We also discuss the numerical techniques necessary for obtaining an accurate numerical solution for the source function.