606 research outputs found
Plasmonic nanoantennas as integrated coherent perfect absorbers on SOI waveguides for modulators and all-optical switches
The performance of plasmonic nanoantenna structures on top of SOI wire
waveguides as coherent perfect absorbers for modulators and all-optical
switches is explored. The absorption, scattering, reflection and transmission
spectra of gold and aluminum nanoantenna-loaded waveguides were calculated by
means of 3D finite-difference time-domain simulations for single waves
propagating along the waveguide, as well as for standing wave scenarios
composed from two counterpropagating waves. The investigated configurations
showed losses of roughly 1% and extinction ratios greater than 25 dB for
modulator and switching applications, as well as plasmon effects such as strong
field enhancement and localization in the nanoantenna region. The proposed
plasmonic coherent perfect absorbers can be utilized for ultracompact
all-optical switches in coherent networks as well as modulators and can find
applications in sensing or in increasing nonlinear effects.Comment: 10 pages, 6 figure
An ultrafast reconfigurable nanophotonic switch using wavefront shaping of light in a nonlinear nanomaterial
We demonstrate a new concept for reconfigurable nanophotonic devices
exploiting ultrafast nonlinear control of shaped wavefronts in a multimode
nanomaterial consisting of semiconductor nanowires. Femtosecond pulsed laser
excitation of the nanowire mat is shown to provide an efficient nonlinear
mechanism to control both destructive and constructive interference in a shaped
wavefront. Modulations of up to 63% are induced by optical pumping, due to a
combination of multimode dephasing and induced transient absorption. We show
that part of the nonlinear phase dynamics can be inverted to provide a
dynamical revival of the wavefront into an optimized spot with up to 18%
increase of the peak to background ratio caused by pulsed laser excitation. The
concepts of multimode nonlinear switching demonstrated here are generally
extendable to other photonic and plasmonic systems and enable new avenues for
ultrafast and reconfigurable nanophotonic devices.Comment: 18 pages, 6 figure
Mesoscopic light transport by very strong collective multiple scattering in nanowire mats
Under the extreme condition of the scattering length being much shorter than the wavelength, light transport in random media is strongly modified by mesoscopic interference, and can even be halted in an effect known as Anderson localization. Anderson localization in three dimensions has recently been realized for acoustic waves and for cold atoms. Mats of disordered, high-refractive-index semiconductor nanowires are one of the strongest three-dimensional scattering materials for light, but localization has not been shown. Here, we use statistical methods originally developed for microwave waveguides to demonstrate that transport of light through nanowire mats is strongly correlated and governed by mesoscopic interference contributions. Our results confirm the contribution of only a few open modes to the transmission
Observation of Intensity Statistics of Light Transmitted Through 3D Random Media
We experimentally observe the spatial intensity statistics of light
transmitted through three-dimensional isotropic scattering media. The intensity
distributions measured through layers consisting of zinc oxide nanoparticles
differ significantly from the usual Rayleigh statistics associated with
speckle, and instead are in agreement with the predictions of mesoscopic
transport theory, taking into account the known material parameters of the
samples. Consistent with the measured spatial intensity fluctuations, the total
transmission fluctuates. The magnitude of the fluctuations in the total
transmission is smaller than expected on the basis of quasi-one-dimensional
(1D) transport theory, which indicates that quasi-1D theories cannot fully
describe these open three-dimensional media.Comment: 4 pages 3 figure
Transparent conducting oxides for active hybrid metamaterial devices
We present here a study of the combined nonlinear response of plasmonic antenna—transparent conducting oxide hybrids for activation of metamaterial devices. Nanoantenna layers consisting of randomly positioned gold nanodisk dimers are fabricated using hole-mask lithography. The nanoantenna layers are covered with a 20 nm thin layer of transparent conducting oxide (TCO). We investigate the response of atomic layer deposited aluminum-doped zinc oxide (AZO) next to indium–tin oxide (ITO) produced using sputter coating. We show that our results are in agreement with the hypothesis of fast electron-mediated cooling, facilitated by the Ohmic interface between the gold nanodisks and the TCO substrate, which appears a universal mechanism for providing a new hybrid functionality to active metamaterial device
Partial nonlinear reciprocity breaking through ultrafast dynamics in a random photonic medium
We demonstrate that ultrafast nonlinear dynamics gives rise to reciprocity
breaking in a random photonic medium. Reciprocity breaking is observed via the
suppression of coherent backscattering, a manifestation of weak localization of
light. The effect is observed in a pump-probe configuration where the pump
induces an ultrafast step-change of the refractive index during the dwell time
of the probe light in the material. The dynamical suppression of coherent
backscattering is reproduced well by a multiple scattering Monte Carlo
simulation. Ultrafast reciprocity breaking provides a distinct mechanism in
nonlinear optical media which opens up avenues for the active manipulation of
mesoscopic transport, random lasers, and photon localization.Comment: 5 pages, 4 figure
Spatial Modulation Microscopy for Real-Time Imaging of Plasmonic Nanoparticles and Cells
Spatial modulation microscopy is a technique originally developed for
quantitative spectroscopy of individual nano-objects. Here, a parallel
implementation of the spatial modulation microscopy technique is demonstrated
based on a line detector capable of demodulation at kHz frequencies. The
capabilities of the imaging system are shown using an array of plasmonic
nanoantennas and dendritic cells incubated with gold nanoparticles.Comment: 3 pages, 4 figure
Browsing throughout pregnancy:The longitudinal course of social media use during pregnancy
BackgroundThe number of people using social media has substantially increased over the past years. Previous studies have shown associations between social media overuse and mental health problems during pregnancy. The current study evaluates changes in social media use during pregnancy.MethodsPregnant women were recruited at their first antenatal appointment between January 2020 and July 2022 (N = 1135). The time spent on social media, frequency of social media use and problematic social media use, using the Bergen Social Media Addiction Scale (BSMAS), were assessed at 12, 20 and 28 weeks of pregnancy. Pearson r correlations and repeated measures ANOVAs were performed to assess possible changes in social media use over the course of pregnancy. Lastly, we stratified social media use throughout pregnancy for parity.ResultsThere was a significant change in social media use over time, for the time spent on social media, frequency of social media use and problematic social media use. Mean social media scores were the lowest at 12 weeks of pregnancy and increased significantly at 20 weeks of pregnancy, after which they remained stable at 28 weeks. Compared to multiparous women, primiparous women spent more time on social media at 20 weeks of pregnancy, but not at 12 or 28 weeks.ConclusionBecause overuse of social media has been associated with poor mental health, healthcare professionals should be aware of the intensity of social media use throughout pregnancy.<br/
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