590 research outputs found
Coherence effects in propagation through photonic crystals
We have analytically studied how a partially coherent quasi plane wave is affected by a photonic crystal structure including a grating. The analysis is presented for spatial and temporal cases showing the possibility to determine the coherence characteristics of the pulse.
Spontaneous and Stimulated Raman Scattering near Metal Nanostructures in the Ultrafast, High-Intensity regime
The inclusion of atomic inversion in Raman scattering can significantly alter
field dynamics in plasmonic settings. Our calculations show that large local
fields and femtosecond pulses combine to yield: (i) population inversion within
hot spots; (ii) gain saturation; and (iii) conversion efficiencies
characterized by a switch-like transition to the stimulated regime that spans
twelve orders of magnitude. While in Raman scattering atomic inversion is
usually neglected, we demonstrate that in some circumstances full accounting of
the dynamics of the Bloch vector is required
Harmonic generation and energy transport in dielectric and semiconductors at visible and UV wavelengths: the case of GaP
We study inhibition of absorption, transparency, energy and momentum
transport of the inhomogeneous component of harmonic pulses in dielectrics and
semiconductors, at visible and UV wavelengths, focusing on materials like GaP.
In these spectral regions GaP is characterized by large absorption, metallic
behavior or a combination of both. We show that phase locking causes the
generated inhomogeneous signals to propagate through a bulk metallic medium
without being absorbed, that is occurs even in centrosymmetric materials via
the magnetic Lorentz force, and that the transport of energy and momentum is
quite peculiar and seemingly anomalous. These results make it clear that there
are new opportunities in ultrafast nonlinear optics and nano-plasmonics in new
wavelength ranges.Comment: 16 pages, 5 figures, 1 vide
Enhanced second harmonic generation from resonant GaAs gratings
We study second harmonic generation in nonlinear, GaAs gratings. We find
large enhancement of conversion efficiency when the pump field excites the
guided mode resonances of the grating. Under these circumstances the spectrum
near the pump wavelength displays sharp resonances characterized by dramatic
enhancements of local fields and favorable conditions for second harmonic
generation, even in regimes of strong linear absorption at the harmonic
wavelength. In particular, in a GaAs grating pumped at 1064nm, we predict
second harmonic conversion efficiencies approximately five orders of magnitude
larger than conversion rates achievable in either bulk or etalon structures of
the same material.Comment: 8 page
Oblique frozen modes in periodic layered media
We study the classical scattering problem of a plane electromagnetic wave
incident on the surface of semi-infinite periodic stratified media
incorporating anisotropic dielectric layers with special oblique orientation of
the anisotropy axes. We demonstrate that an obliquely incident light, upon
entering the periodic slab, gets converted into an abnormal grazing mode with
huge amplitude and zero normal component of the group velocity. This mode
cannot be represented as a superposition of extended and evanescent
contributions. Instead, it is related to a general (non-Bloch) Floquet
eigenmode with the amplitude diverging linearly with the distance from the slab
boundary. Remarkably, the slab reflectivity in such a situation can be very
low, which means an almost 100% conversion of the incident light into the
axially frozen mode with the electromagnetic energy density exceeding that of
the incident wave by several orders of magnitude. The effect can be realized at
any desirable frequency, including optical and UV frequency range. The only
essential physical requirement is the presence of dielectric layers with proper
oblique orientation of the anisotropy axes. Some practical aspects of this
phenomenon are considered.Comment: text and 9 figure
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
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