65 research outputs found
Hyperbolic carbon nanoforest for phase matching of ordinary and backward electromagnetic waves: second harmonic generation
We show that deliberately engineered dispersive metamaterial slab can enable
the co-existence and phase matching of contra-propagating ordinary fundamental
and extraordinary backward second harmonic surface electromagnetic modes.
Energy flux and phase velocity are contra-directed in the backward waves which
is the phenomenon that gives rise to unique nonlinear optical propagation
processes. We show that frequencies, phase, and group velocities, as well as
nanowaveguide losses inherent to the electromagnetic modes supported by such
metamaterial, can be tailored to maximize conversion of frequencies and to
reverse propagation direction of the generated wave. Such a possibility, which
is of paramount importance for nonlinear photonics, is proved with a numerical
model of the hyperbolic metamaterial made of carbon nanotubes standing on the
metal surface. Extraordinary properties of the backward-wave second harmonic
generation in the reflection direction and of the corresponding frequency
doubling metareflector in the THz are investigated with a focus on the pulsed
regime.Comment: 6 pages, 5 figures. arXiv admin note: text overlap with
arXiv:1602.0249
Ultranarrow resonance peaks in the transmission and reflection spectra of a photonic crystal cavity with Raman gain
The Raman gain of a probe light in a three-state -scheme placed
into a defect of a one-dimensional photonic crystal is studied theoretically.
We show that there exists a pump intensity range, where the transmission and
reflection spectra of the probe field exhibit \textit{simultaneously} occurring
narrow peaks (resonances) whose position is determined by the Raman resonance.
Transmission and reflection coefficients can be larger than unity at pump
intensities of order tens of W/cm. When the pump intensity is
outside this region, the peak in the transmission spectrum turns into a narrow
dip. The nature of narrow resonances is attributed to a drastic dispersion of
the nonlinear refractive index in the vicinity of the Raman transition, which
leads to a significant reduction of the group velocity of the probe wave.Comment: 9 pages, 3 figure
Geometric phase and o-mode blue shift in a chiral anisotropic medium inside a Fabry-P\'erot cavity
Anomalous spectral shift of transmission peaks is observed in a
Fabry--P\'erot cavity filled with a chiral anisotropic medium. The effective
refractive index value resides out of the interval between the ordinary and the
extraordinary refractive indices. The spectral shift is explained by
contribution of a geometric phase. The problem is solved analytically using the
approximate Jones matrix method, numerically using the accurate Berreman method
and geometrically using the generalized Mauguin--Poincar\'e rolling cone
method. The -mode blue shift is measured for a
4-methoxybenzylidene-4'--butylaniline twisted--nematic layer inside the
Fabry--P\'erot cavity. The twist is electrically induced due to the
homeoplanar--twisted configuration transition in an ionic-surfactant-doped
liquid crystal layer. Experimental evidence confirms the validity of the
theoretical model.Comment: the text is available both in English (Timofeev2015en.tex) and in
Russian (download: other formats - source - Timofeev2015ru.tex,
Timofeev2015rus.pdf
Coherent control of light-pulse propagation in a Raman induced grating
We study light-pulse propagation in a dynamically controllable periodic structure (grating)
resulting from Raman interaction of a weak probe pulse with a standing-wave pump and a
second control laser field inN-type four-level atomic media. The grating is induced due to
periodic spatial modulation of the Raman gain in a standing pump field (Raman gain grating).
We show that it is possible to control both the probe pulse amplitude and the group velocity of
the pulse from subluminal to superluminal by varying the pump or control field. Such a grating is
of interest forall-optical switches and transistors
Ienversionless gain in an optically-dense resonant Doppler-broadened medium
Resonant nonlinear-optical interference processes in four-level
Doppler-broadened media are studied. Specific features of amplification and
optical switching of short-wavelength radiation in a strongly-absorbing
resonant gas under coherent quantum control with two longer wavelength
radiations, are investigated. The major outcomes are illustrated with virtual
experiments aimed at inversionless short-wavelength amplification, which also
address deficiencies in this regard in recent experiments. With numerical
simulations related to the proposed experiment in optically-dense sodium dimer
vapor, we show optimal condition for optical switching and the expected gain of
the probe radiation, which is above the oscillation threshold.Comment: 7 pages, 12 eps figures. Video/audio clips of the related virtual
experiments are available on http://kirensky.krasn.ru/popov/opa/opa.ht
Inversionless gain in a three-level system driven by a strong field and collisions
Inversionless gain in a three-level system driven by a strong external field
and by collisions with a buffer gas is investigated. The mechanism of
populating of the upper laser level contributed by the collision transfer as
well as by relaxation caused by a buffer gas is discussed in detail. Explicit
formulae for analysis of optimal conditions are derived. The mechanism
developed here for the incoherent pump could be generalized to other systems.Comment: RevTeX, 9 pages, 4 eps figure
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