539 research outputs found
Free-Space Graphics with Electrically Driven Levitated Light Scatterers
Levitation of optical scatterers provides a new mean to develop free-space
volumetric displays. The principle is to illuminate a levitating particle
displaced at high velocity in three dimensions (3D) to create images based on
persistence of vision (POV). Light scattered by the particle can be observed
all around the volumetric display and therefore provides a true 3D image that
does not rely on interference effects and remains insensitive to the angle of
observation. The challenge is to control with a high accuracy and at high speed
the trajectory of the particle in three dimensions. Systems that use light to
generate free-space images either in plasma or with a bead are strictly
dependent of the scanning method used. Mechanical systems are required to scan
the particles in the volume which weakens the time dynamics. Here we use
electrically driven planar Paul traps (PPTs) to control the trajectory of
electrically charged particles. A single gold particle colloid is manipulated
in three dimensions through AC and DC electrical voltages applied to a PPT.
Electric voltages can be modulated at high frequencies (150 kHz) and allow for
a high speed displacement of particles without moving any other system
component. The optical scattering of the particle in levitation yields
free-space images that are imaged with conventional optics. The trajectory of
the particle is entirely encoded in the electric voltage and driven through
stationary planar electrodes. We show in this paper, the proof-of-concept for
the generation of 3D free space graphics with a single electrically scanned
particle
Purcell factor of Mie resonators featuring electric and magnetic modes
We present a modal approach to compute the Purcell factor in Mie resonators
exhibiting both electric and magnetic resonances. The analytic expressions of
the normal modes are used to calculate the effective volumes. We show that
important features of the effective volume can be predicted thanks to the
translation-addition coefficients of a displaced dipole. Using our formalism,
it is easy to see that, in general, the Purcell factor of Mie resonators is not
dominated by a single mode, but rather by a large superposition. Finally we
consider a silicon resonator homogeneously doped with electric dipolar
emitters, and we show that the average electric Purcell factor dominates over
the magnetic one
Compact metallo-dielectric optical antenna for ultra directional and enhanced radiative emission
We report the design of highly efficient optical antennas employing a
judicious synthesis of metallic and dielectric materials. In the proposed
scheme, a pair of metallic coupled nanoparticles permits large enhancements in
both excitation strength and radiative decay rates, while a high refractive
index dielectric microsphere is employed to efficiently collect light without
spoiling the emitter quantum efficiency. Our simulations indicate potential
fluorescence rate enhancements of 3 orders of magnitude over the entire optical
frequency range
Mode-balancing far field control of light localization in nanoantennas
Light localization is controlled at a scale of lambda/10 in the harmonic
regime from the far field domain in a plasmonic nanoantenna. The nanoantenna
under study consists of 3 aligned spheres 50 nm in diameter separated by a
distance of 5 nm. By simply tuning the orientation of an incident plane wave,
symmetric and antisymmetric mode-balancing induces a strong enhancement of the
near field intensity in one cavity while nullifying the light intensity in the
other cavity. Furthermore, it is demonstrated that the dipolar moment of a
plasmonic particle can be fully extinguished when strongly coupled with a dimer
of identical nanoparticles. Consequently, optical transparency can be achieved
in an ultra-compact symmetric metallic structure
Evolutionary optimization of all-dielectric magnetic nanoantennas
Magnetic light and matter interactions are generally too weak to be detected,
studied and applied technologically. However, if one can increase the magnetic
power density of light by several orders of magnitude, the coupling between
magnetic light and matter could become of the same order of magnitude as the
coupling with its electric counterpart. For that purpose, photonic nanoantennas
have been proposed, and in particular dielectric nanostructures, to engineer
strong local magnetic field and therefore increase the probability of magnetic
interactions. Unfortunately, dielectric designs suffer from physical
limitations that confine the magnetic hot spot in the core of the material
itself, preventing experimental and technological implementations. Here, we
demonstrate that evolutionary algorithms can overcome such limitations by
designing new dielectric photonic nanoantennas, able to increase and extract
the optical magnetic field from high refractive index materials. We also
demonstrate that the magnetic power density in an evolutionary optimized
dielectric nanostructure can be increased by a factor 5 compared to state of
the art dielectric nanoantennas. In addition, we show that the fine details of
the nanostructure are not critical in reaching these aforementioned features,
as long as the general shape of the motif is maintained. This advocates for the
feasibility of nanofabricating the optimized antennas experimentally and their
subsequent application. By designing all dielectric magnetic antennas that
feature local magnetic hot-spots outside of high refractive index materials,
this work highlights the potential of evolutionary methods to fill the gap
between electric and magnetic light-matter interactions, opening up new
possibilities in many research fields.Comment: 13 pages, 4 figure
Total light absorption in a wide range of incidence by nanostructured metal without plasmons
International audienceMetals structured by nanocavities have recently been demonstrated to efficiently absorb light in a wide range of angle of incidence. It has been assumed that nanovoid plasmons are at the origin of the strong absorption. It is shown in this paper that it is possible to totally absorb incident light without plasmons. To avoid their excitation, a diffraction grating consisting of cylindrical cavities in a metallic substrate is illuminated in transverse electric (TE) polarization. It is found that cylindrical cavities can sustain cavity resonances with a high enhancement of the light intensity, provoking a total absorption of light in a wide range of incidence
Transverse multipolar light-matter couplings in evanescent waves
We present an approach to study the interaction between matter and evanescent
fields. The approach is based on the decomposition of evanescent plane waves
into multipoles of well-defined angular momentum transverse to both decay and
propagation directions. We use the approach to identify the origin of the
recently observed directional coupling of emitters into guided modes, and of
the opposite Zeeman state excitation of atoms near a fiber. We explain how to
rigorously quantify both effects, and show that the directionality and the
difference in excitation rates grow exponentially with the multipolar order of
the light-matter interaction. We also use the approach to study and maximize
the transverse torque exerted by an evanescent plane wave onto a given
spherical absorbing particle. The maximum occurs at the quadrupolar order of
the particle, and for a particular polarization of the plane wave. All the
obtained physical insights can be traced back to the two main features of the
decomposition of evanescent plane waves into transverse multipolar modes: A
polarization independent exponential dominance of modes with large transverse
angular momentum, and a polarization controlled parity selection rule.Comment: Last version with slight changes in the figures and tex
Polarizability Expressions for Predicting Resonances in Plasmonic and Mie Scatterers
Polarizability expressions are commonly used in optics and photonics to model
the light scattering by small particles. Models based on Taylor series of the
scattering coefficients of the particles fail to predict the morphologic
resonances hosted by dielectric particles. Here, we propose to use the
factorization of the special functions appearing in the expression of the Mie
scattering coefficients to derive point-like models. These models can be
applied to reproduce both Mie resonances of dielectric particles and plasmonic
resonances of metallic particles. They provide simple but robust tools to
predict accurately the electric and magnetic Mie resonances in dielectric
particles.Comment: 11 pages, 7 figure
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