527 research outputs found
Local field effect as a function of pulse duration
In this note we give semiclassical consideration of the role of pulse
duration in observation of local field effects in the regime of optical
switching. We show that the main parameter governing local field influence is
the ratio of peak Rabi frequency corresponding to medium inversion and Lorentz
frequency of the medium. To obtain significant local field effect, this
parameter should be near unity that is valid only for long enough pulses. We
also discuss the role of relaxation and pulse shape in this processes.Comment: 4 pages, 3 figure
Optimizing mixing in the Rudner-Levitov lattice
Here we discuss optimization of mixing in finite linear and circular
Rudner-Levitov lattices, i.e., Su-Schrieffer-Heeger lattices with a dissipative
sublattice. We show that presence of exceptional points in the systems spectra
can lead to drastically different scaling of the mixing time with the number of
lattice nodes, varying from quadratic to the logarithmic one. When operating in
the region between the maximal and minimal exceptional points, it is always
possible to restore the logarithmic scaling by choosing the initial state of
the chain. Moreover, for the same localized initial state and values of
parameters, a longer lattice might mix much faster than the shorter one. Also
we demonstrate that an asymmetric circular Rudner-Levitov lattice can preserve
logarithmic scaling of the mixing time for an arbitrary large number of lattice
nodes.Comment: To appear in JOSA B, 202
Single Gradientless Light Beam Drags Particles as Tractor Beams
Usually a light beam pushes a particle when the photons act upon it.We investigate the optical forces by nonparaxial gradientless beams and find that the forces can drag suitable particles all the way towards the light source. The major criterion of realizing the backward dragging force is the strong nonparaxiality of
the light beam, which contributes to the pulling force owing to momentum conservation. The nonparaxiality
of the Bessel beam can be manipulated to possess a dragging force along both the radial longitudinal directions, i.e., a ‘‘tractor beam’’ with stable trajectories is achieved
Electromagnetic interaction of arbitrary radial-dependent anisotropic spheres and improved invisibility for nonlinear-transformation-based cloaks
An analytical method of electromagnetic wave interactions with a general
radially anisotropic cloak is established. It is able to deal with arbitrary
parameters (, , and ) of a
radially anisotropic inhomogeneous shell. The general cloaking condition is
proposed from the wave relations for the first time. We derive the parameters
of a novel class of spherical nonlinear cloaks and examine its invisibility
performance by the proposed method at various nonlinear situations. Spherical
metamaterial cloaks with improved invisibility performance is achieved with
optimal nonlinearity in transformation and core-shell ratio.Comment: 19 pages, 9 figure
Non-resonant terahertz field enhancement in periodically arranged nanoslits
We analyze ultra strong non-resonant field enhancement of THz field in periodic arrays of nanoslits cut in ultrathin metal films. The main feature of our approach is that the slit size and metal film thickness are several orders of magnitude smaller than the wavelength k of the impinging radiation.
Two regimes of operation are found. First, when the grating period, frequency-independent enhancement is observed, accompanied by a very high transmission approaching unity. With high accuracy, this enhancement equals the ratio of P to the slit width w. Second, when the grating
period approaches the THz wavelength but before entering the Raleigh-Wood anomaly, the field enhancement in nanoslit stays close to that in a single isolated slit, i.e., the well-known inversefrequency
dependence. Both regimes are non-resonant and thus extremely broadband. The results are obtained by the microscopic Drude-Lorentz model taking into account retardation processes in the metal film and validated by the finite difference frequency domain method. We expect sensor and modulation applications of the predicted giant broadband field enhancement
Drug resistance and viral tropism in HIV-1 subtype C-infected patients in KwaZulu-Natal, South Africa: implications for future treatment options
Article approval pendingDrug resistance poses a significant challenge for the successful application of highly active antiretroviral therapy (HAART) globally. Furthermore, emergence of HIV-1 isolates that preferentially use CXCR4 as a coreceptor for cell entry, either as a consequence of natural viral evolution or HAART use, may compromise the efficacy of CCR5 antagonists as alternative antiviral therapy
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