706 research outputs found
Lorenz-Mie scattering of focused light via complex focus fields: an analytic treatment
The Lorenz-Mie scattering of a wide class of focused electromagnetic fields
off spherical particles is studied. The focused fields in question are
constructed through complex focal displacements, leading to closed-form
expressions that can exhibit several interesting physical properties, such as
orbital and/or spin angular momentum, spatially-varying polarization, and a
controllable degree of focusing. These fields constitute complete bases that
can be considered as nonparaxial extensions of the standard Laguerre-Gauss
beams and the recently proposed polynomials-of-Gaussians beams. Their analytic
form turns out to lead also to closed-form expressions for their multipolar
expansion. Such expansion can be used to compute the field scattered by a
spherical particle and the resulting forces and torques exerted on it, for any
relative position between the field's focus and the particle.Comment: 11 pages, 7 figure
Crashing with disorder: Reaching the precision limit with tensor-based wavefront shaping
Perturbations in complex media, due to their own dynamical evolution or to
external effects, are often seen as detrimental. Therefore, a common strategy,
especially for telecommunication and imaging applications, is to limit the
sensitivity to those perturbations in order to avoid them. Here, we instead
consider crashing straight into them in order to maximize the interaction
between light and the perturbations and thus produce the largest change in
output intensity. Our work hinges on the innovative use of tensor-based
techniques, presently at the forefront of machine learning explorations, to
study intensity-based measurements where its quadratic relationship to the
field prevents the use of standard matrix methods. With this tensor-based
framework, we are able to identify the optimal crashing channel which maximizes
the change in its output intensity distribution and the Fisher information
encoded in it about a given perturbation. We further demonstrate experimentally
its superiority for robust and precise sensing applications. Additionally, we
derive the appropriate strategy to reach the precision limit for
intensity-based measurements leading to an increase in Fisher information by
more than four orders of magnitude with respect to the mean for random
wavefronts when measured with the pixels of a camera
Shaping Single Photons through Multimode Optical Fibers using Mechanical Perturbations
The capacity of information delivered by single photons is boosted by
encoding high-dimensional quantum dits in their transverse shape. Transporting
such high-dimensional quantum dits in optical networks may be accomplished
using multimode optical fibers, which support the low-loss transmission of
multiple spatial modes over existing infrastructure. However, when photons
propagate through a multimode fiber their transverse shape gets scrambled
because of mode mixing and modal interference. This is usually corrected using
free-space spatial light modulators, inhibiting a robust all-fiber operation.
In this work, we demonstrate an all-fiber approach for controlling the shape of
single photons and the spatial correlations between entangled photon pairs,
using carefully controlled mechanical perturbations of the fiber. We optimize
these perturbations to localize the spatial distribution of a single photon or
the spatial correlations of photon pairs in a single spot, enhancing the signal
in the optimized spot by over an order of magnitude. Using the same approach we
show a similar enhancement for coupling light from a multimode fiber into a
single-mode fiber
Structural Characterization of Mono and Dihydroxylated Umbelliferone Derivatives
Coumarin derivatives are a class of compounds with a pronounced wide range of applications, especially in biological activities, in the medicine, pharmacology, cosmetics, coatings and food industry. Their potential applications are highly dependent on the nature of the substituents attached to their nucleus. These substituents modulate their photochemical and photophysical properties, as well as their interactions in their crystalline form, which largely determines the final field of application. Therefore, in this work a series of mono and dihydroxylated coumarin derivatives with different chemical substituents were synthesized and characterized by UV-Visible spectroscopy, thermal analysis (differential scanning calorimetry (DSC) and TGA), 1H NMR and X-Ray Diffraction to identify limitations and possibilities as a function of the molecular structure for expanding their applications in polymer science.This research was funded by the Basque Government within the framework ELKARTEK through the research project KK-2018/00108 and KK-2019/00077. This work was also funded by the Ministry of Economy and Competitiveness—Spain (MINECO) through the research Projects RTC-2016-4887-4 and RTI2018-096636-J-100 within the framework of the National Programme for Research Aimed at the Challenges of Society
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