Enhanced and controllable nonlinear effects in composite with aligned gold spheroid arrays

The linear and nonlinear optical properties of composite containing aligned prolate spheroid nanoparticles embedded in a dielectric host are studied as a function of depolarization factor. It is shown that the effective third-order nonlinear susceptibility of the composite can be significantly enhanced with respect to the linear optical properties, due to a combination of varying nanoparticle shape and interparticle space. The susceptibility enhancement is up to four orders larger compared to the spherical case. The susceptibility enhancement of the host is finally comparable to the inclusion after choosing property structure parameters. The geometry-dependent susceptibility enhancement can lead to an improved figure of merit for nonlinear absorption.

Hybrid nanoarchitectured core shell plasmonic structures with tunable optical properties

Interest in patterned polymer-based flexible nanodevices and sub-100 nm metal and transparent conducting nanostructured electrodes have led us to modify the traditional nanoimprint lithography technique to enable fabrication of an array of sub-100 nm diameter electrode structures. Transparent conducting electrodes (TCOs) are fabricated by coating one or multiple TCO layers of choice on top of a polymer nanostructured scaffold of appropriate dimension. By optimizing the thickness of each of these layers one may tune and optimize the trade-off between the conductivity and transparency of the sample. Incorporation of plasmonic materials such as Ag leads to interplay of localized and tunable surface plasmon resonances within the TCO structures. At plasmon resonance the reflection of the sample is minimized and absorption in the TCO structures dominates. Experimental and simulated reflection spectra of these structures are in good agreement, including the appearance of sharp spectral features that are absent in a simple planar analog. The simulated Brewster angle of the nanopillars decreases compared to the planar reference sample by up to 10-13 degrees depending on the height of the pillars and indicates a reduced effective refractive index. The depolarization factor obtained by ellipsometry is about 0.05, as anticipated for ellipsoidal pillars.

Nonlinear Optical Properties of Spheroidal Metallic Inclusions in a Dielectric Medium

A model for linear and nonlinear optical properties of a composite material consisting of spheroidal metal inclusions embedded in a host medium has been formulated using an effective medium approach. Both aligned and randomly oriented spheroids have been considered, and the results obtained showed a considerable difference between the two situations. Numerical calculations for metallic Au inclusions in a glass matrix have shown that the linear absorption in the case of aligned spheroids with their symmetry axis parallel to the z-axis is largely dependent on the depolarization factor, exhibiting an absorption in the vicinity of 500 nm when the depolarization factor in the direction parallel to the rotational symmetry axis is small. This structure shifts progressively to higher wavelengths when this depolarization factor is increased. In the case of randomly oriented spheroids, contributions from the different particle depolarization factors are present and prominent structures in the linear absorption appear in the long wavelength region, beyond 700 nm. Nonlinear optical properties for both aligned and randomly oriented spheroids also show a strong dependence on the depolarization factor and significant enhancements of these properties can be observed, suggesting possible tailoring of composite properties for various applications.

Grain shape effects on dielectric and electrical properties of rocks

Recently there has been a considerable interest in the effect of anisotropy in the grain shape in the electrical and dielectrical properties of rocks and other inhomogeneous media (Sen 1981a, b; Sen et al, 1981; Mendelson and Cohen, 1982; and Kenyon, 1983). In this note I point out that equation (34) of Mendelson and Cohen (MC) is incorrect. The dc limit of MC equation (34) for the conductivity of rock σ, in terms of porosity ϕ and water conductivity [Formula: see text], gives [Formula: see text] or [Formula: see text] where [Formula: see text] L is the depolarization factor along the principal axis of spheroidal grain and 〈 〉 denotes an average over the distribution in L. This value of [Formula: see text] is in disagreement with the correct value of m in equation (28) of MC [equation (6) below]. [When the sign mistakes in equations MC (33)–(34) are corrected, [Formula: see text]. This agrees with equation (6) below for the case when L has a single value and averaging is redundant.] This inconsistency arises from an incorrect replacement of the inverse of an average in MC equation (33) by an average of inverses. The corrected form of MC equation (33) is [Formula: see text] where ε and [Formula: see text] are the dielectric constants of the mixture and of the matrix, respectively. The dielectric constant [Formula: see text] is complex, [Formula: see text] is real, [Formula: see text] is the permittivity of vacuum, σ the conductivity, ω the angular frequency. The last factor in the right‐hand side of the equation was replaced incorrectly by the average of the inverse, which is incorrect in general. Note that in the dc limit equation (4) above gives [Formula: see text] and, by integration, [Formula: see text] where [Formula: see text] is the dc conductivity of water, σ(0) is the dc conductivity of formation, and [Formula: see text]