Optical second harmonic generation from a thin chiral film

We present a simple model for calculating the second-order optical response of a film of chiral molecules. The difference in the output signal for right or left circularly polarized input is analyzed. A strong enhancement in the normalized differential signal is found for p-polarized output. This is due to the existence of Brewster angles which are slightly different for R or L circular input. This feature has no analog in the linear signal, since in that case the two Brewster angles coincide

Bound state spectroscopy of he adsorbed on NaCl(001): Band structure effects

The interaction between atoms and surfaces may be probed by bound state resonance spectroscopy. The experiments are usually interpreted within the free particle picture which assumes that the energy-momentum relation of atoms adsorbed onto a surface is described by 2D parabolic bands. We calculate and analyze the band structure of an atom adsorbed on a model corrugated surface and follow its behavior as the interaction potential evolves from weakly to strongly corrugated. Besides the expected reduction of degeneracy and development of gaps, we obtained a sizable correction to the bound state energies. We employ our results to reanalyze the available experiments on the system He-NaCl(001)

Scaling of light scattered from fractal aggregates at resonance

Due to the scale invariance of fractal aggregates, light scattered from them often decays as a power of the scattering wave vector. The exponent in this power law has been usually interpreted as the geometrical fractal dimension. However, the validity of this interpretation is questionable for frequencies close to the resonances of the system, for which multiple scattering becomes important. In this work we calculate the dipole moments optically induced in fractal aggregates and the corresponding self-consistent field, as well as the electromagnetic normal modes. To this end, we develop a multiresolution hierarchical representation of the aggregate that allows the study of large systems taking fully into account the long range of the interactions. We analyze the scaling properties of the dynamically induced dipolar distribution. We find that under resonant conditions, scaling with the geometric fractal dimension is only observed for systems much larger than a length scale that is related to the linewidth of each individual resonance. The relevance to this result for the interpretation of light scattering experiments is discussed

Local field effects in the dynamical response of Ag

We evaluate the local field effect for an Ag crystal within the "Swiss cheese" model employing different approximations for the intra-band screening. In this model the inter-band transitions are modeled through polarizable entities with appropriate polarizability localized at the lattice sites of the crystal. Their mutual interactions are screened by the dielectric response of the conduction electrons. We assume a homogeneous electron gas described by either nonlocal hydrodynamic or Lindhard dielectric functions or by a local Drude response. We calculate the screened dipole-dipole interaction tensor and find that it increases with the degree of spatial dispersion. We identify the local field effects on the macroscopic dielectric function and conclude that they depend very strongly on the non-locality of the intra-band screening

Surface plasmon dispersion at silver single-crystal surfaces

We develop a model for the calculation of screening at the surface of single Ag crystals, including the response of both conduction and bound electrons. We obtain the electron-energy-loss spectra on the low index faces, and from it, the corresponding surface plasmon (SP) dispersion relations. Our results depend strongly on the face orientation and, for Ag(110), and also on the propagation direction. With an appropriate choice of surface density profile for the conduction electrons, our model yields large positive SP dispersions, in qualitative agreement with experiment. [S0163-1829(99)11631-X]

Second-harmonic generation from spherical particles

We calculate the nonlinear dipole and quadrupole moments induced at the second-harmonic (SW) frequency 2 omega in a small dielectric sphere by an inhomogeneous monochromatic electric field of frequency omega. We neglect finite-size effects and assume that the selvedge region of the sphere is thin enough so that the surface may be considered locally flat. The second-order dipole displays resonances corresponding to the excitation of dipolar and quadrupolar plasmons at w and a dipolar plasmon at 2 omega, besides the resonances in the nonlinear surface response parameters a, b, and f. The second-order quadrupole, on the other hand, has resonances corresponding to those of a, b, and f, and to the excitation of dipolar surface plasmons at omega only. Depending on the relation between the size of the sphere and the spatial scale of variation of the field, the SH radiation may be dominated by either dipolar or quadrupolar scattering, with a crossover region. As an application, we calculate the SH scattering of a Si sphere lying at various distances above a dielectric substrate

MINIMUM ENERGY CONFIGURATIONS OF ATOMS ADSORBED ON A LATTICE

The minimum energy arrangements of atoms adsorbed on a crystalline surface display a very rich set of geometries originated from the competition between the adsorbate-adsorbate interaction, and the tendency to occupy the most favorable adsorption sites over the substrate. We develop a method to obtain these geometries for rational coverages assuming the adsorbates occupy symmetric sites and that they form a lattice commensurate with the substrate, allowing for multi-atomic primitive cells. We obtain results for adsorption on a square lattice with truncated-dipolar interactions. We propose a new truncation scheme which we compare with previous ones, and we explore the effects of changing the range of the potential. The ordered phases we obtain agree with experiments performed for K over Ir(001) and Cs over Rh(001). Furthermore, our results supply some insight on the absence of observed ordered phases for some rational coverages

REFLECTANCE OF NONLOCAL CONDUCTING SUPERLATTICES

We calculate the p-polarized reflectance spectra of a semi-infinite superlattice made up of alternating spatially dispersive conducting layers, accounting exactly within a hydrodynamic model, for the propagation of plasma waves. Besides the expected structure originated from the infinite-superlattice bulk-plasma resonances, we find an extra series of peaks which arise from the semi-infinite-superlattice surface resonances. The latter originate from standing plasma waves at the surface layer, whose resonant frequencies are larger than those in the interior layers due to confinement effects

TRANSFER-MATRIX APPROACH TO THE OPTICAL REFLECTANCE OF NONLOCAL PERIODIC SUPERLATTICES

A generalized transfer matrix is applied to calculate the reflectance of a semi-infinite periodic superlattice made up of spatially dispersive conducting layers, accounting for the propagation of plasma waves allowed by non-locality. The field inside the superlattice is written as a superposition of the two outgoing solutions of the bulk dispersion relation, with amplitudes given by the electromagnetic boundary conditions supplemented by additional boundary conditions. The discrepancies of the used formalism with that of Trutschel et al. are discussed

Minimum energy 2D patterns of atoms adsorbed on a hexagonal lattice

We obtain the lowest energy 2D arrangements of atoms adsorbed on a hexagonal lattice, assuming rational coverage and a repulsive dipolar adsorbate-adsorbate interaction. To this end we exhaustively explore the ordered arrangements compatible with the coverage, including those that have multiatomic unit cells. For some coverages (theta=1/3, 1/4 and 1/7) we find a well defined ground state, and for others a nearly infinite degeneracy related to the possibility of creating dense arrays of linear defects with a negligible energy cost. We compare our results with some experimental determinations of surface structures in alkali overlayers on fcc (111) and hcp (0001) metal faces. Except for those systems that form islands, we have found agreement between our predicted ground states and experiment. Furthermore, no ordered structures with the coverages of our near degenerate states have been observed