Adel Rahmani

University of Technology Sydney , Sydney, New South Wales, Australia

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Publications (67)193.52 Total impact

  • Patrick C Chaumet, Adel Rahmani
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    ABSTRACT: Controlled optical manipulation of a single dielectric nanoparticle is achieved with a bowtie nanoantenna placed at the end of the probe of a near-field scanning microscope.
    Nature Nanotechnology 04/2014; 9(4):252-3. · 31.17 Impact Factor
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    ABSTRACT: We present a form of the discrete dipole approximation for electromagnetic scattering computations in time domain. We show that the introduction of complex frequencies, through the Laplace transform, significantly improves the computation time. We also show that the Laplace transform and its inverse can be combined to extract the field inside a scatterer at a real resonance frequency.
    Physical Review E 12/2013; 88(6-1):063303. · 2.31 Impact Factor
  • Patrick C. Chaumet, Adel Rahmani
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    ABSTRACT: We present a theoretical and numerical study of the optical binding and optical torque between two Rayleigh particles with arbitrary, complex, scalar dielectric permittivity and magnetic permeability. We use a computational approach based on the discrete dipole approximation to derive the optical force and torque experienced by the particles when illuminated by a linearly or circularly polarized plane wave. We show that optical binding between magnetodielectic particles is qualitatively different from the traditional case involving dielectric particles only. In particular, we show that for certain configurations, the system of two magnetodielectric particles will experience a long-range optical torque whose amplitude envelope does not decay with the separation between the particles.
    Physical review. B, Condensed matter 05/2013; 87(19). · 3.77 Impact Factor
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    ABSTRACT: We study the radiation dynamics of an electric dipole source placed near or inside a discrete invisibility cloak. We show that the main features of radiation dynamics can be understood in terms of the interaction of the source with a nonideal cloak in which local-field effects associated with the discrete geometry play a crucial role. As a result, radiation dynamics in a discrete cloak can differ drastically from what a source would experience in an ideal, continuous cloak. This can lead, for instance, to an enhancement of the emission by the cloak, thus making the source more visible to an outside observer than it would be without the cloak. The two main physical mechanisms for enhanced, or inhibited, radiation dynamics are the coupling of the source to leaky modes inside the cloak, and the coupling of the source with the lattice of the discrete cloak, via the local field. We also explore the robustness of the effect to material dispersion and losses.
    Physical review. B, Condensed matter 01/2013; 87(4). · 3.77 Impact Factor
  • Source
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    ABSTRACT: We demonstrate a method to reduce the mode volume of optical micro/nanocavities by positioning an opaque microtip in close proximity of the structures. This concept is used to blueshift the resonance of an active photonic crystal nanocavity by up to 16 nm. This tuning range is shown to be about 10 times larger than the redshift achieved with a bare dielectric microtip of the same size and shape. By imagining materials or multilayered devices with the ability to become transparent and opaque under external control, the blue and redshifts of the resonance would become possible with a single perturbing device.
    Applied Physics Letters 07/2012; 101(5). · 3.52 Impact Factor
  • Source
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    ABSTRACT: We study electromagnetic forces and torques on a discrete spherical invisibility cloak under time-harmonic illumination. We consider the influence of material absorption and losses, and we show that while the impact of absorption on the optical force remains confined to frequencies near the absorption peak, its impact on the electromagnetic torque experienced by the cloak is spectrally broader and follows the spectrum of the absorption cross section of the cloak. We also investigate the mechanical shielding of a test particle within the cloak. We find that even an imperfect cloak can reduce the radiation pressure on the particle significantly; however, under certain conditions the force on the particle can be stronger than it would be in the absence of the cloak.
    Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics 05/2012; 85(5).
  • Source
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    ABSTRACT: We study the near-field probing of the slow Bloch laser mode of a photonic crystal by a bowtie nano-aperture (BNA) positioned at the end of a metal-coated fiber probe. We show that the BNA acts as a polarizing nanoprobe allowing us to extract information about the polarization of the near-field of the slow-light mode, without causing any significant perturbation of the lasing process. Near-field experiments reveal a spatial resolution better than λ/20 and a polarization ratio as strong as 110. We also demonstrate that the collection efficiency is two orders of magnitude larger for the BNA than for a 200 nm large circular aperture opened at the apex of the same metal-coated fiber tip. The BNA allows for overcoming one of the main limitations of SNOM linked to the well-known trade off between resolution and signal-to-noise ratio.
    Optics Express 02/2012; 20(4):4124-35. · 3.55 Impact Factor
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    ABSTRACT: We study, in time domain, the exchange of momentum between an electromagnetic pulse and a three-dimensional, discrete, spherical invisibility cloak. We find that a discrete cloak, initially at rest, would experience an electromagnetic force due to the pulse but would acquire zero net momentum and net displacement. On the other hand, we find that while the cloak may manage to conceal an object and shroud it from the electromagnetic forces associated with the pulse, the cloak itself can experience optomechanical stress on a scale much larger than the object would in the absence of the cloak. We also consider the effects of material dispersion and losses on the electromagnetic forces experienced by the cloak and show that they lead to a transfer of momentum from the pulse to the cloak.
    Physical Review A 09/2011; 84(3). · 3.04 Impact Factor
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    ABSTRACT: We report on the near- and far-field investigation of the Slow Bloch Mode associated with the Γ-point of the Brillouin zone, for an active honeycomb lattice photonic crystal, using near-field scanning optical microscopy.
    04/2011;
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    ABSTRACT: We propose to use a localized Γ-point slow Bloch mode in a 2D-Photonic Crystal (PC) membrane to realize an efficient surface emitting source. This device can be used as a quantum photonic device, e.g. a single photon source. The physical mechanisms to increase the Q/V factor and to improve the directivity of the PC microcavity rely on a fine tuning of the geometry in the three directions of space. The PC lateral mirrors are first engineered in order to optimize photons confinement. Then, the effect of a Bragg mirror below the 2DPC membrane is investigated in terms of out-of-plane leakages and far field emission pattern. This photonic heterostructure allows for a strong lateral confinement of photons, with a modal volume of a few (λ/n)3 and a Purcell factor up to 80, as calculated by two different numerical methods. We finally discuss the efficiency of the single photon source for different collection set-up.
    Optics Express 03/2011; 19(6):5014-25. · 3.55 Impact Factor
  • C. G. Poulton, A. Rahmani, M. J. Steel
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    ABSTRACT: We study the radiation dynamics of an electric line current source in a homogeneous, magneto-dielectric cylinder. We find that radiation by the source is most enhanced by maximizing the magnetic response of the cylinder.
    01/2011;
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    ABSTRACT: We study dipole emission inside a homogeneous, magnetic sphere. For fixed refractive index, the largest emission rate for an electric source is observed, in general, when the magnetic permeability is maximized. The corresponding result for a magnetic source follows by symmetry. © 2010 Optical Society of America OCIS codes: 290.0290 Scattering, 160.3918 Metamaterials It is well-established that the radiation of sources depends on the physical environment in the vicinity of the source (1). In particular, a source placed in an electromagnetic cavity can have its emission enhanced or suppressed, depending on the cavity properties. Until recently it was thought possible to tune only the electric properties of the cavity (via the permittivity ε), however metamaterials offer the possibility of controlling both the electric and magnetic responses of a medium, leading to markedly different radiation dynamics (2). We study here the emission of sources placed in metamaterial cavities, in which the magnetic properties may be controlled by changing the permeability μ. We investigate the circumstances in which emission may be enhanced or suppressed, and outline how the inclusion of magnetic effects leads to differences in the physics of radiating sources. Consider a classical oscillating electric dipole, with normalized dipole moment p, located at position r0 in vacuum. We denote by Γ∞ the rate at which the dipole radiates energy. If we now consider the same dipole placed in a given environment, the emission rate changes to Γenv given by Γenv Γ∞ = 1 +
    01/2011;
  • Source
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    ABSTRACT: We present a general approach, based on the discrete dipole approximation (DDA), for the computation of the exchange of momentum between light and a magnetodielectric, three-dimensional object with arbitrary geometry and linear permittivity and permeability tensors in time domain. The method can handle objects with an arbitrary shape, including objects with dispersive dielectric and/or magnetic material responses.
    Optics Express 01/2011; 19(3):2466-75. · 3.55 Impact Factor
  • M.J. Steel, P.C. Chaumet, A. Rahmani
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    ABSTRACT: We study the radiation dynamics of a dipole inside a discrete invisibility cloak. The dynamics differ drastically from the case of an ideal, continuous cloak, with the cloak sometimes enhancing the visibility of the source.
    Quantum Electronics Conference & Lasers and Electro-Optics (CLEO/IQEC/PACIFIC RIM), 2011; 01/2011
  • Source
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    ABSTRACT: We report on the near- and far-field investigation of the slow Bloch modes associated with the Γ point of the Brillouin zone, for a honeycomb lattice photonic crystal, using near-field scanning optical microscopy (NSOM) and infra-red CCD camera. The array of doughnut-shaped monopolar mode (mode M) inside each unit cell, predicted previously by numerical simulation, is experimentally observed in the near-field by means of a metal-coated NSOM tip. In far-field, we detect the azimuthal polarization of the doughnut laser beam due to destructive and constructive interference of the mode radiating from the surface (mode TEM(01*)). A divergence of 2° for the laser beam and a mode size of (12.8 ± 1) µm for the slow Bloch mode at the surface of the crystal are also estimated.
    Optics Express 12/2010; 18(26):26879-86. · 3.55 Impact Factor
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    ABSTRACT: A method is developed to enhance the amplitudes of the non-propagating evanescent orders of resonant dielectric gratings. The origin of these resonances is analyzed in detail. The method relies on interactions between stacked gratings with different periods, and so a formalism is developed to model such stacks mathematically. In addition, a theoretical approach is developed to design gratings that enhance or blaze desired orders. These orders, controlled independently by incident fields from different angles, interfere and are optimized to produce steerable sub-Rayleigh field concentrations on a surface. These spots may function as a virtual scanning probe for non-invasive sub-Rayleigh microscopy. Optimization is conducted using a Monte Carlo Markov chain, and spots are generated which are both 1 order of magnitude narrower than the free space Rayleigh limit and robust to noise in the incident fields.
    Journal of the Optical Society of America B 11/2010; 27(12):2580-2594. · 2.21 Impact Factor
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    ABSTRACT: We develop a way to enhance the amplitudes of the nonpropagating evanescent orders of resonant dielectric gratings. We use this blazing to design gratings with spectra tailored to generate steerable sub-Rayleigh field concentrations on a surface. We investigate the enhancement and customization of evanescent fields necessary to create a virtual and passive scanning probe with no moving parts. Spot size can be decreased 1 order of magnitude below the free-space Rayleigh limit.
    Optics Letters 09/2010; 35(17):2846-8. · 3.39 Impact Factor
  • Source
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    ABSTRACT: We develop a general computational approach, based on the discrete dipole approximation, for the study of radiation dynamics near or inside an object with arbitrary linear dielectric permittivity, and magnetic permeability tensors. Our method can account for dispersion and losses and provides insight on the role of local-field corrections in discrete magnetodielectric structures. We illustrate our method in the case of a source inside a magneto-dielectric, isotropic sphere for which the spontaneous emission rate of a source can be computed analytically. We show that our approach is in excellent agreement with the exact result, providing an approach capable of handling both the electric and magnetic response of advanced metamaterials.
    Optics Express 04/2010; 18(8):8499-504. · 3.55 Impact Factor
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    ABSTRACT: We develop a general theoretical and computational framework to describe, in time domain, the exchange of momentum between light and arbitrary three-dimensional objects. Our formulation can be used to study the time evolution of optical forces on any object with linear material response, including inhomogeneous, dispersive, and absorbing dielectrics and metals. We illustrate our approach by studying the behavior of the Abraham force on an object illuminated by a sequence of electromagnetic pulses.
    Physical Review A 02/2010; 81(2). · 3.04 Impact Factor
  • Source
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    ABSTRACT: An ensemble of spherical particles with arbitrary dielectric permittivity and magnetic permeability was considered in the dipole approximation. Each particle was described by com-plex electric and magnetic polarizabilities. A computational approach based on the coupled dipole method, also called the discrete dipole approximation, was used to derive the optical force experienced by each particle due to an incident electromagnetic field and the fields scat-tered by all other particles. This approach is general and can handle material dispersion and losses. In order to illustrate this approach, we studied the case of two spherical particles sepa-rated by a distance d, and illuminated by an incident plane wave whose wave vector is normal to the axis of the particles. We computed the optical force experienced by each particle in the direction of the beam (radiation pressure), and perpendicular to the beam (optical binding) for particles with positive and negative refractive indices. We also considered the effect of material losses.
    02/2010;

Publication Stats

760 Citations
193.52 Total Impact Points

Institutions

  • 2008–2014
    • University of Technology Sydney 
      • School of Mathematical Sciences
      Sydney, New South Wales, Australia
  • 2010
    • University of Sydney
      • School of Physics
      Sydney, New South Wales, Australia
  • 2007–2010
    • Macquarie University
      • • MQ Photonics Research Centre
      • • Centre for Ultra-high Bandwidth Devices for Optical Systems
      Sydney, New South Wales, Australia
  • 2003–2010
    • Ecole Centrale de Lyon
      • Institut des Nanotechnologies de Lyon
      Rhône-Alpes, France
  • 2009
    • Aix-Marseille Université
      • Institut Fresnel (UMR 7249 FRESNEL)
      Marseille, Provence-Alpes-Cote d'Azur, France
  • 2005–2009
    • Université Paul Cézanne
      Aix, Provence-Alpes-Côte d'Azur, France
  • 2004
    • Spanish National Research Council
      • Instituto de Ciencia de Materiales de Madrid
      Madrid, Madrid, Spain
  • 2001–2004
    • National Institute of Standards and Technology
      Maryland, United States
  • 1996–2004
    • French National Centre for Scientific Research
      Lutetia Parisorum, Île-de-France, France