arXiv subjects

Ayan Banerjee

Publications and source records attributed to Ayan Banerjee.

At least 199 records · Page 11Linked to original sources

arXiv2016

Braneworld gravastars admitting conformal motion

In this work, we study the Mazur and Mottola gravastar model within the context of Randall-Sundrum II type braneworld scenario, based on the fact that our four dimensional space-time is a three-brane, embedded in a five dimensional bulk. We present exact solutions of the modified field equations in each of the three regions making up the gravastar, namely, (I) the core, (II) the shell, and (III) the vacuum exterior. The junction conditions at each interface are fulfilled and we further explore interesting physical properties such as length and energy and entropy of the spherical distribution.

gr-qc↗

arXiv2015

Stability of Thin-Shell Wormholes from Noncommutative BTZ Black Hole

In this paper, we construct thin-shell wormholes in (2+1)-dimensions from noncommutative BTZ black hole by applying the cut-and-paste procedure implemented by Visser. We calculate the surface stresses localized at the wormhole throat by using the Darmois-Israel formalism, and we find that the wormholes are supported by matter violating the energy conditions. In order to explore the dynamical analysis of the wormhole throat, we consider that the matter at the shell is supported by dark energy equation of state P = wρwith w < 0. The stability analysis is carried out of these wormholes to linearized spherically symmetric perturbations around static solutions. Preserving the symmetry we also consider the linearized radial perturbation around static solution to investigate the stability of wormholes which explored by the parameter β(speed of sound).

gr-qc↗

arXiv2014

Exact solutions in (2 + 1)-dimensional anti-de Sitter space-time admitting a linear or non-linear equation of state

Gravitational analyzes in lower dimensions has become a field of active research interest ever since Banados, Teitelboim and Zanelli (BTZ) (Phys. Rev. Lett. 69, 1849, 1992) proved the existence of a black hole solution in (2 + 1) dimensions. The BTZ metric has inspired many investigators to develop and analyze circularly symmetric stellar models which can be matched to the exterior BTZ metric. We have obtained two new classes of solutions for a (2 + 1)-dimensional anisotropic star in anti-de Sitter background space-time which have been obtained by assuming that the equation of state (EOS) describing the material composition of the star could either be linear or non-linear in nature. By matching the interior solution to the BTZ exterior metric with zero spin, we have demonstrated that the solutions provided here are regular and well-behaved at the stellar interior.

gr-qc↗

arXiv2014

Charged star in (2+1)-dimensional gravity

We obtain a new class of exact solutions for the Einstein-Maxwell system in static spherically symmetric charged star in (2+1)-dimensional gravity. In order to obtain the analytical solutions we treat the matter distribution anisotropic in nature admitting linear or nonlinear equation of state and the electric field intensity was specified. By choosing a suitable choice of mass function m(r), it is possible to integrate the system in closed form. All the solution, which are obtained in both linear and nonlinear cases are regular at the center and well behaved in the stellar interior.

gr-qc↗

arXiv2014

Simultaneous detection of rotational and translational motion in optical tweezers by measurement of backscattered intensity

We describe a simple yet powerful technique of simultaneously measuring both translational and rotational motion of mesoscopic particles in optical tweezers by measuring the backscattered intensity on a quadrant photodiode (QPD). While the measurement of translational motion by taking the difference of the backscattered intensity incident on adjacent quadrants of a QPD is well-known, we demonstrate that rotational motion can be measured very precisely by taking the difference between the diagonal quadrants. The latter measurement eliminates the translational component entirely, and leads to a detection sensitivity of around 50 mdeg at S/N of 2 for angular motion of a driven micro-rod. The technique is also able to resolve the translational and rotational Brownian motion components of the micro-rod in an unperturbed trap, and can be very useful in measuring translation-rotation coupling of micro-objects induced by hydrodynamic interactions.

physics.optics↗

arXiv2013

Noncommutative Wormholes in $f(R)$ Gravity with Lorentzian Distribution

In this paper, we derive some new exact solutions of static wormholes in $f(R)$ gravity supported by the matter possesses Lorentizian density distribution of a particle-like gravitational source. We derive the wormhole's solutions in two possible schemes for a given Lorentzian distribution: assuming an astrophysically viable $F(R)$ function such as a power-law form and discuss several solutions corresponding to different values of the exponent (here $F =\frac{df}{dR}$). In the second scheme, we consider particular form of two shape functions and have reconstructed f(R) in both cases. We have discussed all the solutions with graphical point of view.

gr-qc↗

arXiv2013

Stability of charged thin-shell wormholes in (2 + 1) dimensions

In this paper we construct charged thin-shell wormholes in (2+1)-dimensions applying the cut-and -paste technique implemented by Visser, from a BTZ black hole which was discovered by Banados, Teitelboim and Zanelli, and the surface stress are determined using the Darmois-Israel formalism at the wormhole throat. We analyzed the stability of the shell considering phantom-energy or generalised Chaplygin gas equation of state for the exotic matter at the throat. We also discussed the linearized stability of charged thin-shell wormholes around the static solution.

gr-qc↗

arXiv2013

Enhanced topological phase and spin Hall shifts in an optical trap

The spin orbit interaction (SOI) of light has been in the focus in recent times because of fundamental consequences and potential applications in diverse systems ranging from inhomogeneous anisotropic media to engineered plasmonics and metamaterial strutures. Here we demonstrate perhaps one of the simplest means to realize SOI and the Spin Hall Shift (SHS) using a standard Gaussian TEM$_{00}$ beam in an optical trap. Our system exploits the versatility and interference generated in a stratified medium to control and manipulate SOI and transfer the resulting angular momentum to optically trapped micro-particles. We show that even such a simple setup can lead to an order of magnitude enhancement in the SHS compared to the sub-wavelength shifts typically obtained. Importantly, this leads to controlled rotation of mesoscopic particles using a fundamental Gaussian beam lacking any intrinsic angular momentum.

physics.optics↗

arXiv2013

Micro-OptoMechanical Movements (MOMs) with SoftOxometalates (SOMs): Controlled Motion of Single Soft-Oxometalate Pea-pods Using Exotic Optical Potentials

An important challenge in the field of materials design and synthesis is to deliberately design mesoscopic objects starting from well-defined precursors and inducing directed movements in them to emulate biological processes. Recently, mesoscopic metal-oxide based Soft Oxo Metalates (SOMs) have been synthesized from well-defined molecular precursors transcending the regime of translational periodicity. Here we show that it is actually possible to controllably move such an asymmetric SOM-with the shape of a `pea-pod' along complex paths using tailor-made sophisticated optical potentials created by spin-orbit interaction due to a tightly focused linearly polarized Gaussian beam propagating through stratified media in an optical trap. We demonstrate motion of individual trapped SOMs along circular paths of more than 15 $μ$m in a perfectly controlled manner by simply varying the input polarization of the trapping laser. Such controlled motion can have a wide range of application starting from catalysis to the construction of dynamic mesoscopic architectures.

cond-mat.mes-hall↗

arXiv2013

Finch-Skea star in (2+1) dimensions

The Bañados, Teitelboim and Zanelli\cite{BTZ} solution corresponding to the exterior space-time of a black hole in $(2+1)$ dimensions has been found to be very useful to understand various aspects relating to the gravitational field of a black hole. We present here a class of interior solutions corresponding to the BTZ exterior by making use of a model presented by Finch and Skea\cite{Finch} which was earlier found to be relevant for the description realistic stars in $(3+1)$ dimensions. We show physical viability of the model in lower dimensions as well.

gr-qc↗

arXiv2013

Stability of Non-asymptotically flat thin-shell wormholes in generalized dilaton-axion gravity

We construct a new type of thin-shell wormhole for non-asymptotically flat charged black holes in generalized dilaton-axion gravity inspired by low-energy string theory using cut-and-paste technique. We have shown that this thin shell wormhole is stable. The most striking feature of our model is that the total amount of exotic matter needed to support the wormhole can be reduced as desired with the suitable choice of the value of a parameter. Various other aspects of thin-shell wormhole are also analyzed.

gr-qc↗

arXiv2013

Controlled and Continuous Patterning of Organic and Inorganic Materials by Induced Nucleation in an Optical Tweezers

We demonstrate for the first time controlled patterning by inducing nucleation of material from a dense aqueous dispersion or solution in an optical tweezers. A hot spot is formed on a glass surface by the trapping laser due to which a water vapor bubble is formed causing Gibbs-Marangoni convection of material around the bubble. This results in accretion of material around the bubble, which eventually nucleates into a crystalline state of the material. The nucleation site, when moved by translating the microscope stage of the optical tweezers apparatus, forms a pattern. We have demonstrated the technique using exotic inorganic materials such as soft oxometalates, and organic materials such as glycine, paracetamol, and a fluorescent dye such as perylene. We have written patterns over lengths of nearly 1 mm at the rate of 1 Hz, with best resolution of about 1 micron. The technique has potential for a wide range of applications ranging from solution processed printable electronics to controlled catalysis.

cond-mat.mtrl-sci↗

arXiv2013

Controlled transportation of mesoscopic particles by enhanced spin orbit interaction of light in an optical trap

We study the effects of the spin orbit interaction (SOI) of light in an optical trap and show that the propagation of the tightly focused trapping beam in a stratified medium can lead to significantly enhanced SOI. For a plane polarized incident beam the SOI manifests itself by giving rise to a strong anisotropic linear diattenuation effect which produces polarization-dependent off-axis high intensity side lobes near the focal plane of the trap. Single micron-sized asymmetric particles can be trapped in the side lobes, and transported over circular paths by a rotation of the plane of input polarization. We demonstrate such controlled motion on single pea-pod shaped single soft oxometalate (SOM) particles of dimension around $1\times 0.5μ$m over lengths up to $\sim$15 $μ$m . The observed effects are supported by calculations of the intensity profiles based on a variation of the Debye-Wolf approach. The enhanced SOI could thus be used as a generic means of transporting mesoscopic asymmetric particles in an optical trap without the use of complex optical beams or changing the alignment of the beam into the trap.

physics.optics↗

arXiv2012

Mueller matrix polarimetry of plasmon resonant silver nano-rods: biomedical prospects

Fundamental understanding of the light-matter interaction in the context of nano-particles is immensely bene- fited by the study of geometry dependent tunable Localized Surface Plasmon Resonance (LSPR) and has been demonstrated to have potential applications in various areas of science. The polarization characteristics of LSPR in addition to spectroscopic tuning can be suitably exploited in such systems as contrast enhancement mech- anisms and control parameters. Such polarization characteristics like diattenuation and retardance have been studied here using a novel combination of Muller-matrix polarimetry with the T-matrix matrix approach for silver nano-rods to show unprecedented control and sensitivity to local refractive index variations. The study carried out over various aspect ratios for a constant equal volume sphere radius shows the presence of longitu- dinal (dipolar and quadrupolar) and transverse (dipolar) resonances; arising due to differential contribution of polarizabilities in two directions. The overlap regions of these resonances and the resonances themselves exhibit enhanced retardance and diattenuation respectively. The spectral and amplitude tunability of these polarimetric parameters through the aspect ratios to span from the minimum to maximum ([0, 1] in the case of diattenuation and [0, π] in the case of retardance) presents a novel result that could be used to tailor systems for study of biological media. On the other hand, the high sensitivity of diattenuation dip (caused by equal contribution of polarizabilities) could be possibly used for medium characterization and bio-sensing or bio-imaging studies.

physics.optics↗

arXiv2012

Spin orbit interaction of light mediated by scattering from plasmonic nano-structures

The spin orbit interactions (SOI) of light mediated by single scattering from plasmon resonant metal nanoparticles (nanorods and nanospheres) are investigated using explicit theory based on Jones and Stokes-Mueller polarimetry formalism. The individual SOI effects are analyzed and interpreted via the Mueller matrix-derived, polarimetry characteristics, namely, diattenuation d and retardance δ. The results demonstrate that each of the contributing SOI effects can be controllably enhanced by exploiting the interference of two neighboring modes in plasmonic nanostructures (orthogonal electric dipolar modes in rods or electric dipolar and quadrupolar modes in spheres).

physics.optics↗

arXiv2012

Singularity free stars in (2+1) dimensions

We present some new types of non-singular model for anisotropic stars with constant $Λ$ and variable $Λ$ based on the Krori and Barua (KB) metric in $(2+1)$ dimensions. The solutions obtained here satisfy all the regularity conditions and its simple analytical form helps us to study the various physical properties of the configuration.

gr-qc↗

arXiv2012

Self assembly of microparticles in stable ring structures in an optical trap

Micro-particle self assembly under the influence of optical forces produced by higher order optical beams or by projection of a hologram into the trapping volume is well known. In this paper, we report the spontaneous formation of a ring of identical microspheres (each with diameter 1.1 $μ$m) in conventional single beam optical tweezers with a usual TEM$_{00}$ Gaussian beam coupled into a sample chamber having standing wave geometry with a cover slip and glass slide. The effects of different experimental parameters on the ring formation are studied extensively. The experimental observations are backed by theoretical simulations based on a plane wave decomposition of the forward and backward propagating Gaussian beams. The ring patterns are shown to be caused due to geomterical aberrations produced by focusing the Gaussian beam using a high numerical aperture microscope objective into stratified media. It is found that the thickness of the stratified media and the standing wave geometry itself play a critical role in formation of stable ring structures. These structures could be used in the study of optical binding, as well as biological interactions between cells in an optical trap.

physics.optics↗

arXiv2012

Probing the dynamics of an optically trapped particle by phase sensitive back focal plane interferometry

The dynamics of an optically trapped particle are often determined by measuring intensity shifts of the back-scattered light from the particle using position sensitive detectors. We present a technique which measures the phase of the back-scattered light using balanced detection in an external Mach-Zender interferometer scheme where we separate out and beat the scattered light from the bead and that from the top surface of our trapping chamber. The technique has improved axial motion resolution over intensity-based detection, and can also be used to measure lateral motion of the trapped particle. In addition, we are able to track the Brownian motion of trapped 1 and 3 $μ$m diameter beads from the phase jitter and show that, similar to intensity-based measurements, phase measurements can also be used to simultaneously determine displacements of the trapped bead as well as the spring constant of the trap. For lateral displacements, we have matched our experimental results with a simulation of the overall phase contour of the back-scattered light for lateral displacements by using plane wave decomposition in conjunction with Mie scattering theory. The position resolution is limited by path drifts of the interferometer which we have presently reduced to obtain a displacement resolution of around 2 nm for 1.1 $μ$m diameter probes by locking the interferometer to a frequency stabilized diode laser.

physics.optics↗