263 research outputs found
A Dynamical Model of Harmonic Generation in Centrosymmetric Semiconductors
We study second and third harmonic generation in centrosymmetric
semiconductors at visible and UV wavelengths in bulk and cavity environments.
Second harmonic generation is due to a combination of symmetry breaking, the
magnetic portion of the Lorentz force, and quadrupolar contributions that
impart peculiar features to the angular dependence of the generated signals, in
analogy to what occurs in metals. The material is assumed to have a non-zero,
third order nonlinearity that gives rise to most of the third harmonic signal.
Using the parameters of bulk Silicon we predict that cavity environments can
significantly modify second harmonic generation (390nm) with dramatic
improvements for third harmonic generation (266nm). This occurs despite the
fact that the harmonics may be tuned to a wavelength range where the dielectric
function of the material is negative: a phase locking mechanism binds the pump
to the generated signals and inhibits their absorption. These results point the
way to novel uses and flexibility of materials like Silicon as nonlinear media
in the visible and UV ranges
Second and Third Harmonic Generation in Metal-Based Nanostructures
We present a new theoretical approach to the study of second and third
harmonic generation from metallic nanostructures and nanocavities filled with a
nonlinear material, in the ultrashort pulse regime. We model the metal as a
two-component medium, using the hydrodynamic model to describe free electrons,
and Lorentz oscillators to account for core electron contributions to both the
linear dielectric constant and to harmonic generation. The active nonlinear
medium that may fill a metallic nanocavity, or be positioned between metallic
layers in a stack, is also modeled using Lorentz oscillators and surface
phenomena due to symmetry breaking are taken into account. We study the effects
of incident TE- and TM-polarized fields and show that a simple re-examination
of the basic equations reveals additional exploitable dynamical features of
nonlinear frequency conversion in plasmonic nanostructures.Comment: 33 pages, including 11 figures and 74 references; corrected
affiliations and some typo
Reevaluation of radiation reaction and consequences for light-matter interactions at the nanoscale
In the context of electromagnetism and nonlinear optical interactions damping
is generally introduced as a phenomenological, viscous term that dissipates
energy, proportional to the temporal derivative of the polarization. Here, we
follow the radiation reaction method presented in [G. W. Ford and R. F.
O'Connell, Phys. Lett. A, 157, 217 (1991)], which applies to non-relativistic
electrons of finite size, to introduce an explicit reaction force in the
Newtonian equation of motion, and derive a hydrodynamic equation that offers
new insight on the influence of damping in generic plasmas, metal-based and/or
dielectric structures. In these settings, we find new damping-dependent linear
and nonlinear source terms that suggest the damping coefficient is proportional
to the local charge density, and nonlocal contributions that stem from the
spatial derivative of the magnetic field and discuss the conditions that could
modify both linear and nonlinear electromagnetic responses.Comment: 11 pages, 1 figure, 19 reference
Tailoring Metallodielectric Structures for Super Resolution and Superguiding Applications in the Visible and Near IR Ranges
We discuss propagation effects in realistic, transparent, metallo-dielectric
photonic band gap structures in the context of negative refraction and
super-resolution in the visible and near infrared ranges. In the resonance
tunneling regime, we find that for transverse-magnetic incident polarization,
field localization effects contribute to a waveguiding phenomenon that makes it
possible for the light to remain confined within a small fraction of a
wavelength, without any transverse boundaries, due to the suppression of
diffraction. This effect is related to negative refraction of the Poynting
vector inside each metal layer, balanced by normal refraction inside the
adjacent dielectric layer: The degree of field localization and material
dispersion together determine the total momentum that resides within any given
layer, and thus the direction of energy flow. We find that the transport of
evanescent wave vectors is mediated by the excitation of quasi-stationary, low
group velocity surface waves responsible for relatively large losses. As
representative examples we consider transparent metallo-dielectric stacks such
as Ag/TiO2 and Ag/GaP and show in detail how to obtain the optimum conditions
for high transmittance of both propagating and evanescent modes for
super-guiding and super resolution applications across the visible and near IR
ranges. Finally, we study the influence of gain on super-resolution. We find
that the introduction of gain can compensate the losses caused by the
excitation of surface plasmons, improves the resolving characteristics of the
lens, and leads to gain-tunable super-resolution
Spatio-temporal instabilities for counterpropagating waves in periodic media.
Nonlinear evolution of coupled forward and backward fields in a multi-layered film is numerically investigated. We examine the role of longitudinal and transverse modulation instabilities in media of finite length with a homogeneous nonlinear susceptibilityfont face="Symbol"c/font((3)). The numerical solution of the nonlinear equations by a beam-propagation method that handles backward waves is described
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