8,350 research outputs found
Nonlinear acousto-magneto-plasmonics
We review the recent progress in experimental and theoretical research of
interactions between the acoustic, magnetic and plasmonic transients in hybrid
metal-ferromagnet multilayer structures excited by ultrashort laser pulses. The
main focus is on understanding the nonlinear aspects of the acoustic dynamics
in materials as well as the peculiarities in the nonlinear optical and
magneto-optical response. For example, the nonlinear optical detection is
illustrated in details by probing the static magneto-optical second harmonic
generation in gold-cobalt-silver trilayer structures in Kretschmann geometry.
Furthermore, we show experimentally how the nonlinear reshaping of giant
ultrashort acoustic pulses propagating in gold can be quantified by
time-resolved plasmonic interferometry and how these ultrashort optical pulses
dynamically modulate the optical nonlinearities. The effective medium
approximation for the optical properties of hybrid multilayers facilitates the
understanding of novel optical detection techniques. In the discussion we
highlight recent works on the nonlinear magneto-elastic interactions, and
strain-induced effects in semiconductor quantum dots.Comment: 30 pages, 12 figures, to be published as a Topical Review in the
Journal of Optic
Multilayer optical learning networks
A new approach to learning in a multilayer optical neural network based on holographically interconnected nonlinear devices is presented. The proposed network can learn the interconnections that form a distributed representation of a desired pattern transformation operation. The interconnections are formed in an adaptive and self-aligning fashioias volume holographic gratings in photorefractive crystals. Parallel arrays of globally space-integrated inner products diffracted by the interconnecting hologram illuminate arrays of nonlinear Fabry-Perot etalons for fast thresholding of the transformed patterns. A phase conjugated reference wave interferes with a backward propagating error signal to form holographic interference patterns which are time integrated in the volume of a photorefractive crystal to modify slowly and learn the appropriate self-aligning interconnections. This multilayer system performs an approximate implementation of the backpropagation learning procedure in a massively parallel high-speed nonlinear optical network
Fourier Optics approach to imaging with sub-wavelength resolution through metal-dielectric multilayers
Metal-dielectric layered stacks for imaging with sub-wavelength resolution
are regarded as linear isoplanatic systems - a concept popular in Fourier
Optics and in scalar diffraction theory. In this context, a layered flat lens
is a one-dimensional spatial filter characterised by the point spread function.
However, depending on the model of the source, the definition of the point
spread function for multilayers with sub-wavelength resolution may be
formulated in several ways. Here, a distinction is made between a soft source
and hard electric or magnetic sources. Each of these definitions leads to a
different meaning of perfect imaging. It is shown that some simple
interpretations of the PSF, such as the relation of its width to the resolution
of the imaging system are ambiguous for the multilayers with sub-wavelenth
resolution. These differences must be observed in point spread function
engineering of layered systems with sub-wavelength sized PSF
Resonant Elastic Soft X-Ray Scattering
Resonant (elastic) soft x-ray scattering (RSXS) offers a unique element,
site, and valence specific probe to study spatial modulations of charge, spin,
and orbital degrees of freedom in solids on the nanoscopic length scale. It
cannot only be used to investigate single crystalline materials. This method
also enables to examine electronic ordering phenomena in thin films and to zoom
into electronic properties emerging at buried interfaces in artificial
heterostructures. During the last 20 years, this technique, which combines
x-ray scattering with x-ray absorption spectroscopy, has developed into a
powerful probe to study electronic ordering phenomena in complex materials and
furthermore delivers important information on the electronic structure of
condensed matter. This review provides an introduction to the technique, covers
the progress in experimental equipment, and gives a survey on recent RSXS
studies of ordering in correlated electron systems and at interfaces
Accelerated Carrier Recombination by Grain Boundary/Edge Defects in MBE Grown Transition Metal Dichalcogenides
Defect-carrier interaction in transition metal dichalcogenides (TMDs) play
important roles in carrier relaxation dynamics and carrier transport, which
determines the performance of electronic devices. With femtosecond laser
time-resolved spectroscopy, we investigated the effect of grain boundary/edge
defects on the ultrafast dynamics of photoexcited carrier in MBE grown MoTe2
and MoSe2. We found that, comparing with exfoliated samples, carrier
recombination rate in MBE grown samples accelerates by about 50 times. We
attribute this striking difference to the existence of abundant grain
boundary/edge defects in MBE grown samples, which can serve as effective
recombination centers for the photoexcited carriers. We also observed coherent
acoustic phonons in both exfoliated and MBE grown MoTe2, indicating strong
electron-phonon coupling in this materials. Our measured sound velocity agrees
well with previously reported result of theoretical calculation. Our findings
provide useful reference for the fundamental parameters: carrier lifetime and
sound velocity, reveal the undiscovered carrier recombination effect of grain
boundary/edge defects, both of which will facilitate the defect engineering in
TMD materials for high speed opto-electronics
Incoherent LADAR detection technique to identify and characterize multilayer samples at long-range distances
Ce mémoire décrit le développement d’une technique incohérente de détection LADAR à l’aide d’une diode laser à longueur d’onde accordable afin d’identifier un échantillon multicouches à distance avec une résolution submillimétrique. Les principes de LADAR ainsi que les techniques d’interférométrie utilisés pour la détection d’un échantillon multicouches sont présentés. Par la suite, les concepts théoriques essentiels pour ce mémoire sont décrits, en particulier l’interféromètre à fréquence accordable, la comparaison des mesures prises en réflexion et transmission, et l’effet des mesures prises à un angle d’incidence. La phase expérimentale consistait en une série d’essais en laboratoire pour valider le montage expérimental, ainsi qu’un programme diversifié de mesures extérieures avec une multitude de configurations d’échantillons multicouches. Les résultats concluants démontrent la capacité d’identifier et de définir des échantillons multicouches à distances, incluant lorsque mesurés à un angle d’incidence.This thesis outlines the development of an incoherent LADAR detection technique using a tunable laser diode source to identify and characterize multilayer samples with sub-millimeter resolution at long-range distances. The principles of LADAR and interferometry techniques currently being utilized to detect a stratified medium are first described. This is followed by the theoretical concepts that underline the work of this thesis, where in particular the frequency swept interferometer, the comparison of measurements performed in reflection versus transmission, and the effects of off-axis measurements are explained. The experimental phase consisted of a series of indoor tests to validate the experimental setup and the signal analysis code, and a wide-ranging outdoor measurement programme with numerous configurations of multilayer samples. The results successfully demonstrate the ability to identify and characterize multilayer samples at long-range distances, including when there is an angle of incidence on the substrate
Nanoscale Magnetic Imaging using Circularly Polarized High-Harmonic Radiation
This work demonstrates nanoscale magnetic imaging using bright circularly
polarized high-harmonic radiation. We utilize the magneto-optical contrast of
worm-like magnetic domains in a Co/Pd multilayer structure, obtaining
quantitative amplitude and phase maps by lensless imaging. A
diffraction-limited spatial resolution of 49 nm is achieved with iterative
phase reconstruction enhanced by a holographic mask. Harnessing the unique
coherence of high harmonics, this approach will facilitate quantitative,
element-specific and spatially-resolved studies of ultrafast magnetization
dynamics, advancing both fundamental and applied aspects of nanoscale
magnetism.Comment: Ofer Kfir and Sergey Zayko contributed equally to this work.
Presented in CLEO 2017 (Oral) doi.org/10.1364/CLEO_QELS.2017.FW1H.
Chiral Surface Waves for Enhanced Circular Dichroism
We present a novel chiral sensing platform that combines a one-dimensional
photonic crystal design with a birefringent surface defect. The platform
sustains simultaneous transverse electric and transverse magnetic surface
modes, which are exploited to generate chiral surface waves. The present design
provides homogeneous and superchiral fields of both handednesses over
arbitrarily large areas in a wide spectral range, resulting in the enhancement
of the circular dichroism signal by two orders of magnitude, thus paving the
road toward the successful combination of surface-enhanced spectroscopies and
electromagnetic superchirality.Comment: Added references. Corrected typos. Included new design for broadband
chiral surface wave
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