arXiv subjects

M. R. C. Mahdy

Publications and source records attributed to M. R. C. Mahdy.

22 records · Page 2Linked to original sources

arXiv2017

Consistency of time averaged optical force laws for embedded chiral and achiral objects

Although it is commonly believed that all the volumetric optical force laws should lead to the same total optical force for chiral and achiral objects, this idea has been invalidated in some recent works by investigating several previous experiments involving material background. To identify the exact reason of such significant disagreement, we inspect two tractor beam and one lateral force experiments on using distinct stress tensors (STs). To solve the problems of total force, we propose two consistency conditions of time averaged forces. We demonstrate that exactly at the boundary of an object, the difference of the consistent external Minkowski ST and internal ST of Chu (and Einstein-Laub) is found in agreement with the surface force yielded by Chu (and Einstein-Laub) force only when the background is air rather than a material. We identify this as one of the main reasons (among few other identified reasons) of the disagreements observed for real experiments. Finally, based on the proposed consistency conditions, we demonstrate that: by modifying the Einstein-Laub or Chu formulation, time-averaged STs and volume forces are obtainable those can overcome the aforementioned inconsistencies of real experiments for both chiral and achiral Mie objects embedded in even complex material backgrounds.

physics.optics↗

arXiv2017

Substrate Effect on Plasmonic Cube Dimers: Reversal of Optical Binding Force Induced by Strong Fano Resonance

The behavior of Fano resonance and the reversal of near field optical binding force of dimers over different substrates have not been studied so far. In this work, we observe that if the closely located plasmonic cube homodimers over glass or high permittivity dielectric substrate are illuminated with plane wave polarized parallel to dimer axis, no reversal of optical binding force occurs. But if we apply the same set-up over a plasmonic substrate, stable Fano resonance occurs along with the reversal of near field binding force. It is observed that during such Fano resonance stronger coupling occurs between the dimers and plasmonic substrate along with the strong enhancement of the substrate current. Such near field binding force reversals of plasmonic cube dimers have been explained based on the observed unusual behavior of optical Lorentz force during the induced stronger Fano resonance and the dipole-dipole resonance. Although previously reported reversals of near field optical binding forces were highly sensitive to particle size/shape (i.e. for heterodimers) and inter-particle distance, our configuration provides much relaxation of those parameters and hence should be verified experimentally with simpler experimental set-ups.

physics.optics↗

arXiv2015

A unified theory correcting Einstein-Laub electrodynamics solves dilemmas in the photon momenta and electromagnetic stress tensors

To unify and clarify the persistently debated electromagnetic stress tensors (ST) and photon momenta, we establish a theory inspired by the Einstein-Laub formalism inside an arbitrary macroscopic object immersed in any complex medium. Our generalized Einstein-Laub force and ST yield the total force experienced by any generic macroscopic object due to the internal field interacting with its atoms, charges and molecules. Appropriate scenarios are established for the conservation of a newly proposed momentum that we call non-mechanical generalized Einstein-Laub momentum, along with the kinetic and canonical momenta of photons. Our theory remains valid even in a generally heterogeneous or bounded embedding background medium without resorting to hidden momenta, and unambiguously identifies the existence domain, or validity domain, of the STs and photon momenta proposed to date. This existence domain is the region either outside a macroscopic scatterer with only exterior fields, or at its interior with only inside fields. The appropriate identification of such existence domain constitutes the basis of our unified theory. Finally, a thought experiment is proposed, which shows that the appropriate force and the photon momentum in the embedding medium can also be properly identified if the background is comparatively larger than the embedded scatterer. It also explains the fully different roles of the Abraham and Minkowski photon momenta in the embedding medium. Most importantly, our unified theory reveals that a unique formulation of the momentum conservation law is unfeasible, though a generalized expression of the ST and momentum density is achievable in terms of new concepts that we introduce, namely, the effective polarization and effective magnetization.

physics.optics↗

arXiv2013

On the Relation between Perfect Tunneling and Band Gaps for SNG Metamaterial Structures

In this article, we have proposed a compact classification of isotropic and homogeneous single negative (SNG) electromagnetic metamaterial based perfect tunneling unit cells. This unified classification has been made by means of the band gap theories and properties of the arrays made up of these unit cells. Based on their reported characteristics, we have proposed new structures that simultaneously show perfect tunneling band and complete band gap (CBG-omni directional stop band for both polarizations). Besides, we have identified a kind of perfect tunneling which can be considered as "phase shifted perfect tunneling". Several interesting and new phenomena like Complete Perfect Tunneling (CPT-omni directional perfect tunneling for both polarizations), Band Gap Shifting,CBG in Double Positive (DPS) material range, etc. have been reported with proper physical and mathematical explanations.

physics.optics↗