230 research outputs found
Van der Waals interactions across stratified media
Working at the Lifshitz level, we investigate the van der Waals interactions
across a series of layers with a periodic motif. We derive the complete form of
the van der Waals interaction as an explicit function of the number of periodic
layers. We then compare our result with an approximation based on an
anisotropic-continuum representation of the stratified medium. Satisfactory
agreement between discrete-layer and continuum models is reached only for
thicknesses of ten or more layers.Comment: 9 pages and 4 figure
Dielectric multilayer waveguides for TE and TM mode matching
We analyse theoretically for the first time to our knowledge the perfect
phase matching of guided TE and TM modes with a multilayer waveguide composed
of linear isotropic dielectric materials. Alongside strict investigation into
dispersion relations for multilayer systems, we give an explicit qualitative
explanation for the phenomenon of mode matching on the basis of the standard
one-dimensional homogenization technique, and discuss the minimum number of
layers and the refractive index profile for the proposed device scheme. Direct
applications of the scheme include polarization-insensitive, intermodal
dispersion-free planar propagation, efficient fibre-to-planar waveguide
coupling and, potentially, mode filtering. As a self-sufficient result, we
present compact analytical expressions for the mode dispersion in a finite,
N-period, three-layer dielectric superlattice.Comment: 13 pages with figure
Nonlinear localized waves in a periodic medium
We analyze the existence and stability of nonlinear localized waves in a
periodic medium described by the Kronig-Penney model with a nonlinear defect.
We demonstrate the existence of a novel type of stable nonlinear band-gap
localized states, and also reveal an important physical mechanism of the
oscillatory wave instabilities associated with the band-gap resonances.Comment: 4 pages, 5 figure
The Casimir force and the quantum theory of lossy optical cavities
We present a new derivation of the Casimir force between two parallel plane
mirrors at zero temperature. The two mirrors and the cavity they enclose are
treated as quantum optical networks. They are in general lossy and
characterized by frequency dependent reflection amplitudes. The additional
fluctuations accompanying losses are deduced from expressions of the optical
theorem. A general proof is given for the theorem relating the spectral density
inside the cavity to the reflection amplitudes seen by the inner fields. This
density determines the vacuum radiation pressure and, therefore, the Casimir
force. The force is obtained as an integral over the real frequencies,
including the contribution of evanescent waves besides that of ordinary waves,
and, then, as an integral over imaginary frequencies. The demonstration relies
only on general properties obeyed by real mirrors which also enforce general
constraints for the variation of the Casimir force.Comment: 18 pages, 6 figures, minor amendment
The calculation of thin film parameters from spectroscopic ellipsometry data
Spectroscopic ellipsometry (SE) has proven to be a very powerful diagnostic for thin film characterization, but the results of SE experiments must first be compared with calculations to determine thin film parameters such as film thickness and optical functions. This process requires 4 steps: (1) The quantities measured must be specified and the equivalent calculated parameters identified. (2) The film structure must be modeled, where the number of films is specified and certain characteristics of each layer specified, such as whether or not the film is isotropic or anisotropic, homogeneous or graded. (3) The optical functions of each layer must be specified or parameterized. (4) The data must be compared with the calculated spectra, where a quantifiable figure of merit is used for the comparison. The last step is particularly important because without it, no {open_quotes}goodness of fit{close_quotes} parameter is calculated and one does not know whether or not the calculated spectrum fits the data
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