1,173 research outputs found
Control of LED Emission with Functional Dielectric Metasurfaces
The improvement of light-emitting diodes (LEDs) is one of the major goals of
optoelectronics and photonics research. While emission rate enhancement is
certainly one of the targets, in this regard, for LED integration to complex
photonic devices, one would require to have, additionally, precise control of
the wavefront of the emitted light. Metasurfaces are spatial arrangements of
engineered scatters that may enable this light manipulation capability with
unprecedented resolution. Most of these devices, however, are only able to
function properly under irradiation of light with a large spatial coherence,
typically normally incident lasers. LEDs, on the other hand, have angularly
broad, Lambertian-like emission patterns characterized by a low spatial
coherence, which makes the integration of metasurface devices on LED
architectures extremely challenging. A novel concept for metasurface
integration on LED is proposed, using a cavity to increase the LED spatial
coherence through an angular collimation. Due to the resonant character of the
cavity, extending the spatial coherence of the emitted light does not come at
the price of any reduction in the total emitted power. The experimental
demonstration of the proposed concept is implemented on a GaP LED architecture
including a hybrid metallic-Bragg cavity. By integrating a silicon metasurface
on top we demonstrate two different functionalities of these compact devices:
directional LED emission at a desired angle and LED emission of a vortex beam
with an orbital angular momentum. The presented concept is general, being
applicable to other incoherent light sources and enabling metasurfaces designed
for plane waves to work with incoherent light emitters.Comment: 29 pages, 6 figure
Cavity-induced damping and level shifts in a wide aperture spherical resonator
We calculate explicitly the space dependence of the radiative relaxation
rates and associated level shifts for a dipole placed in the vicinity of the
center of a spherical cavity with a large numerical aperture and a relatively
low finesse. In particular, we give simple and useful analytic formulas for
these quantities, that can be used with arbitrary mirrors transmissions. The
vacuum field in the vicinity of the center of the cavity is actually equivalent
to the one obtained in a microcavity, and this scheme allows one to predict
significant cavity QED effects.Comment: 28 pages, 5 figures. In v2 some references and appendices adde
Preliminary studies for anapole moment measurements in rubidium and francium
Preparations for the anapole measurement in Fr indicate the possibility of
performing a similar measurement in a chain of Rb. The sensitivity analysis
based on a single nucleon model shows the potential for placing strong limits
on the nucleon weak interaction parameters. There are values of the magnetic
fields at much lower values than found before that are insensitive to first
order changes in the field. The anapole moment effect in Rb corresponds to an
equivalent electric field that is eighty times smaller than Fr, but the
stability of the isotopes and the current performance of the dipole trap in the
apparatus, presented here, are encouraging for pursuing the measurment.Comment: 16 pages, 6 figures. Accepted for publication in the J. Phys.
Topological Frequency Conversion in a Driven Dissipative Quantum Cavity
Recent work (PRX 7, 041008) has shown that a spin coupled to two externally
supplied circularly-polarized electromagnetic modes can effectuate a
topological, quantized transfer of photons from one mode to the other. Here we
study the effect in the case when only one of the modes is externally provided,
while the other is a dynamical quantum mechanical cavity mode. Focusing on the
signatures and stability under experimentally accessible conditions, we show
that the effect persists down to the few-photon quantum limit and that it can
be used to generate highly entangled "cat states" of cavity and spin. By tuning
the strength of the external drive to a "sweet spot", the quantized pumping can
arise starting from an empty (zero photon) cavity state. We also find that
inclusion of external noise and dissipation does not suppress but rather
stabilizes the conversion effect, even after multiple cavity modes are taken
into account.Comment: 12 pages, 6 figure
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