47 research outputs found
Nanostratification of optical excitation in self-interacting 1D arrays
The major assumption of the Lorentz-Lorenz theory about uniformity of local
fields and atomic polarization in dense material does not hold in finite groups
of atoms, as we reported earlier [A. E. Kaplan and S. N. Volkov, Phys. Rev.
Lett., v. 101, 133902 (2008)]. The uniformity is broken at sub-wavelength
scale, where the system may exhibit strong stratification of local field and
dipole polarization, with the strata period being much shorter than the
incident wavelength. In this paper, we further develop and advance that theory
for the most fundamental case of one-dimensional arrays, and study nanoscale
excitation of so called "locsitons" and their standing waves (strata) that
result in size-related resonances and related large field enhancement in finite
arrays of atoms. The locsitons may have a whole spectrum of spatial
frequencies, ranging from long waves, to an extent reminiscent of ferromagnetic
domains, -- to super-short waves, with neighboring atoms alternating their
polarizations, which are reminiscent of antiferromagnetic spin patterns. Of
great interest is the new kind of "hybrid" modes of excitation, greatly
departing from any magnetic analogies. We also study differences between
Ising-like near-neighbor approximation and the case where each atom interacts
with all other atoms in the array. We find an infinite number of "exponential
eigenmodes" in the lossless system in the latter case. At certain "magic"
numbers of atoms in the array, the system may exhibit self-induced (but linear
in the field) cancellation of resonant local-field suppression. We also studied
nonlinear modes of locsitons and found optical bistability and hysteresis in an
infinite array for the simplest modes.Comment: 39 pages, 5 figures; v2: Added the Conclusions section, corrected a
typo in Eq. (5.3), corrected minor stylistic and grammatical imperfection
Soliton absorption spectroscopy
We analyze optical soliton propagation in the presence of weak absorption
lines with much narrower linewidths as compared to the soliton spectrum width
using the novel perturbation analysis technique based on an integral
representation in the spectral domain. The stable soliton acquires spectral
modulation that follows the associated index of refraction of the absorber. The
model can be applied to ordinary soliton propagation and to an absorber inside
a passively modelocked laser. In the latter case, a comparison with water vapor
absorption in a femtosecond Cr:ZnSe laser yields a very good agreement with
experiment. Compared to the conventional absorption measurement in a cell of
the same length, the signal is increased by an order of magnitude. The obtained
analytical expressions allow further improving of the sensitivity and
spectroscopic accuracy making the soliton absorption spectroscopy a promising
novel measurement technique.Comment: 9 pages, 7 figures
Enhancement of absorption bistability by trapping light planar metamaterial
We propose to achieve a strong bistable response of a thin layer of a
saturable absorption medium by involving a planar metamaterial specially
designed to bear a high-Q trapped-mode resonance in the infrared region.Comment: 11 pages, 4 figure
Scattering of slow-light gap solitons with charges in a two-level medium
The Maxwell-Bloch system describes a quantum two-level medium interacting
with a classical electromagnetic field by mediation of the the population
density. This population density variation is a purely quantum effect which is
actually at the very origin of nonlinearity. The resulting nonlinear coupling
possesses particularly interesting consequences at the resonance (when the
frequency of the excitation is close to the transition frequency of the
two-level medium) as e.g. slow-light gap solitons that result from the
nonlinear instability of the evanescent wave at the boundary. As nonlinearity
couples the different polarizations of the electromagnetic field, the
slow-light gap soliton is shown to experience effective scattering whith
charges in the medium, allowing it for instance to be trapped or reflected.
This scattering process is understood qualitatively as being governed by a
nonlinear Schroedinger model in an external potential related to the charges
(the electrostatic permanent background component of the field).Comment: RevTex, 14 pages with 5 figures, to appear in J. Phys. A: Math. Theo
Nonreciprocal amplitude-frequency resonant response of metasandwiches “ferrite plate-grating of resonant elements”
New microwave nonreciprocal properties are investigated in “ferrite plate
– grating of resonant elements” metasandwiches arranged along the axis of
a rectangular waveguide in a transverse constant magnetic field. Giant
nonreciprocity in the transmission is observed at the ferromagnetic
resonance frequencies at certain values of the magnetic field under
conditions of a mutual influence between the ferromagnetic and the grating
resonances. In addition, nonreciprocal splitting of the resonance in grating
elements is observed under small magnetic field, which is much less than the
field necessary to the ferromagnetic resonance excitation.
The nonreciprocal transmission does not take place in the case of free
ferrite in the absence of a grating. Sign reversal of the nonreciprocity is
observed, when ferrite transfers to the opposite side of a grating as well
as under certain values of the constant magnetic field, when the sign
reversal of difference between frequencies of the ferromagnetic resonance
and the grating resonance takes place. Nonreciprocal effects are explained
by the interaction between precessing spins in ferrite and a magnetic field
of the surface wave, formed by a grating, and by coupling between the
resonances of grating elements. It has been shown theoretically that
microwaves in waveguide with bianisotropic layer, simulating a grating of
resonant elements, are elliptically or circularly polarized with frequency
and spatially – dependent rotating sense of the microwave magnetic field.
The nonreciprocal effects have been observed for different grating elements:
for both electric dipoles and chiral elements