223 research outputs found
Enhanced photosensitivity in tin-codoped germanosilicate optical fibres
Enhanced photosensitivity is found in Tin-codoped germanosilicate optical fibers. A photo-induced refractive index change (~1.4 x 10-3 times larger than that observed in pure germanosilicate fibers has been demonstrated. Unlike the technique of using Boron-codoping to enhance the photosensitivity of germanosilicate fibers, Tin-doping does not have a significant effect on fiber loss at the important telecommunication window of 1.55µm. High temperature stability of the gratings in Tin-codoped germanosilicate fibers is also much over Boron-codoped fibers
Grating formulation in a phosphorus-doped germanosilicate fibre
Refractive index changes as high as ~5 x 10-4 in a phosphorus-doped germanosilicate fibre were observed for the first time without hydrogen loading during grating formation with a 193 nm laser. Dynamics was studied and it was found that Type IIa gratings was easily formed in this fibre
Large photo-induced index changes in tin-doped phosphosilicate fibre
Strong photosensitive gratings of both type I and II have been demonstrated in germanium-free tin-doped phosphosilicate fibre. An index change of ~1.2 x 10-3 has been achieved in 40 seconds of exposure. This is the first time that such strong gratings were written in a phosphorous-containing silica fibre and that type II gratings were written in a germanium-free fibre
Chirped fibre Bragg gratings fabricated using etched tapers
We have demonstrated a technique which is capable of controllably producing fibre Bragg gratings with arbitrary chirp profiles using etched tapers. Gratings with 4.8nm linear chirp have been produced. Nonlinearly chirped gratings have also been demonstrated
Large photo-induced index changes in Sn-doped germanosilicate fibres
Index change (~1.4 x 10-3) of 3 times larger than in germanosilicate fibres is demonstrated. Both fibre loss at 1.55µm and high temperature stability of the gratings are much improved comparing to those in B-codoped germanosilicate fibres
Dissipative Future Universe without Big Rip
The present study deals with dissipative future universe without big rip in
context of Eckart formalism. The generalized chaplygin gas, characterized by
equation of state , has been considered as
a model for dark energy due to its dark-energy-like evolution at late time. It
is demonstrated that, if the cosmic dark energy behaves like a fluid with
equation of state ; , as well as chaplygin gas
simultaneously then the big rip problem does not arises and the scale factor is
found to be regular for all time.Comment: 6 pages, 2 figures, To appear in Int. J. Theor. Phy
Interacting Modified Variable Chaplygin Gas in Non-flat Universe
A unified model of dark energy and matter is presented using the modified
variable Chaplygin gas for interacting dark energy in a non-flat universe. The
two entities interact with each other non-gravitationally which involves a
coupling constant. Due to dynamic interaction, the variation in this constant
arises that henceforth changes the equations of state of these quantities. We
have derived the effective equations of state corresponding to matter and dark
energy in this interacting model. Moreover, the case of phantom energy is
deduced by putting constraints on the parameters involved.Comment: 9 pages; Accepted for publication in European Physical Journal
Particle motion in the field of a five-dimensional charged black hole
In this paper, we have investigated the geodesics of neutral particles near a
five-dimensional charged black hole using a comparative approach. The effective
potential method is used to determine the location of the horizons and to study
radial and circular trajectories. This also helps us to analyze the stability
of radial and circular orbits. The radius of the innermost stable circular
orbits have also been determined. Contrary to the case of massive particles for
which, the circular orbits may have up to eight possible values of specific
radius, we find that the photons will only have two distinct values for the
specific radii of circular trajectories. Finally we have used the dynamical
systems analysis to determine the critical points and the nature of the
trajectories for the timelike and null geodesics.Comment: 15 pages, accepted for publication in Astrophysics and Space Scienc
Microscopic mechanisms of spin-dependent electric polarization in 3d oxides
We present a short critical overview of different microscopic models for
nonrelativistic and relativistic magnetoelectric coupling including the
so-called "spin current scenario", ab-initio calculations, and several recent
microscopic approaches to a spin-dependent electric polarization in 3d oxides.Comment: 8 pages, 3 figure
Interacting Kasner-type cosmologies
It is well known that Kasner-type cosmologies provide a useful framework for
analyzing the three-dimensional anisotropic expansion because of the
simplification of the anisotropic dynamics. In this paper relativistic
multi-fluid Kasner-type scenarios are studied. We first consider the general
case of a superposition of two ideal cosmic fluids, as well as the particular
cases of non-interacting and interacting ones, by introducing a
phenomenological coupling function . For two-fluid cosmological scenarios
there exist only cosmological scaling solutions, while for three-fluid
configurations there exist not only cosmological scaling ones, but also more
general solutions. In the case of triply interacting cosmic fluids we can have
energy transfer from two fluids to a third one, or energy transfer from one
cosmic fluid to the other two. It is shown that by requiring the positivity of
energy densities there always is a matter component which violates the dominant
energy condition in this kind of anisotropic cosmological scenarios.Comment: Accepted for publication in Astrophysics &Space Science, 8 page
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