115 research outputs found
Resonance tunneling of polaritons in 1-D chain with a single defect
We consider propagation of coupled waves (polaritons) formed by a scalar
electromagnetic wave and excitations of a finite one dimensional chain of
dipoles. It is shown that a microscopic defect (an impurity dipole) embedded in
the chain causes resonance tunneling of the electromagnetic wave with the
frequency within the forbidden band between two polariton branches. We
demonstrate that resonance tunneling occurs due to local polariton states
caused by the defect.Comment: 11 pages, 9 figures (PS-format), RevTe
Local polariton modes and resonant tunneling of electromagnetic waves through periodic Bragg multiple quantum well structures
We study analytically defect polariton states in Bragg multiple-quantum-well
structures and defect induced changes in transmission and reflection spectra.
Defect layers can differ from the host layers in three ways: exciton-light
coupling strength, exciton resonance frequency, and inter-well spacing. We show
that a single defect leads to two local polariton modes in the photonic
bandgap. These modes cause peculiarities in reflection and transmission
spectra. Each type of defect can be reproduced experimentally, and we show that
each of these plays a distinct role in the optical properties of the system.
For some defects, we predict a narrow transmission window in the forbidden gap
at the frequency set by parameters of the defect. We obtain analytical
expressions for corresponding local frequencies as well as for reflection and
transmission coefficients. We show that the presence of the defects leads to
resonant tunneling of the electromagnetic waves via local polariton modes
accompanied by resonant enhancement of the field inside the sample, even when a
realistic absorption is taken into account. On the basis of the results
obtained, we make recommendations regarding the experimental observation of the
effects studied in readily available samples.Comment: 17 pages, 10 figures, RevTex, Submitted to PR
Concept of local polaritons and optical properties of mixed polar crystals
The concept of local polaritons is used to describe optical properties of
mixed crystals in the frequency region of their {\it restrahlen} band. It is
shown that this concept allows for a physically transparent explanation of the
presence of weak features in the spectra of so called one-mode crystals, and
for one-two mode behavior. The previous models were able to explain these
features only with the use of many fitting parameters. We show that under
certain conditions new impurity-induced polariton modes may arise within the
{\it restrahlen} of the host crystals, and study their dispersion laws and
density of states. Particularly, we find that the group velocity of these
excitations is proportional to the concentration of the impurities and can be
thousands of times smaller then the speed of light in vacuum.Comment: 21 pages, 5 figures, RevTex, Phys. Rev. B, 62, 6301 (2000
Spectral engineering with multiple quantum well structures
It is shown that it is possible to significantly modify optical spectra of
Bragg multiple quantum well structures by introducing wells with different
exciton energies. The reflection spectrum of the resulting structures is
characterized by high contrast and tuning possibilities
Local polariton states in impure ionic crystals
We consider the dynamics of an ionic crystal with a single impurity in the
vicinity of the polariton resonance. We show that if the polariton spectrum of
the host crystal allows for a gap between polariton branches, the defect gives
rise to a novel kind of local states with frequencies within the gap. Despite
the atomic size of the impurity we find that new local states are predominated
by long-wavelength polaritons. The properties of these states are shown to be
different from the properties of the well-known vibrational local states. The
difference is due to the singular behavior of the density of states of
polaritons near the low-frequency boundary of the polariton gap. Assuming cubic
simmetry of the defect site we consider a complete set of the local states
arising near the bottom of the polariton gap.Comment: 10 pages, 3 Postscript figures, to be published in Phys. Rev. B 1998,
Vol. 57, No.
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