561 research outputs found
Enhancement of inherent Raman scattering in dielectric nanostructures with electric and magnetic Mie resonances
Resonantly enhanced Raman scattering in dielectric nanostructures has been
recently proven to be an effcient tool for developing nanothermometry and
experimental determination of their mode- composition. In this paper, we
develop a rigorous analytical theory based on the Green's function approach to
calculate the Raman emission from crystalline high-index dielectric
nanoparticles. As an example, we consider silicon nanoparticles which have a
strong Raman response due to active optical phonon modes. We relate enhancement
of Raman signal emission to Purcell effect due to the excitation of Mie modes
inside the nanoparticles. We also employ the numerical approach to the
calculation of inelastic Raman emission in more sophisticated geometries, which
do not allow a straightforward analytical form of the Green's function
description. The Raman response from a silicon nanodisk has been analyzed
within the proposed method, and the contribution of the various Mie modes has
been revealed
Multipolar origin of bound states in the continuum
Metasurfaces based on resonant subwavelength photonic structures enable novel
ways of wavefront control and light focusing, underpinning a new generation of
flat-optics devices. Recently emerged all-dielectric metasurfaces exhibit
high-quality resonances underpinned by the physics of bound states in the
continuum that drives many interesting concepts in photonics. Here we suggest a
novel approach to explain the physics of bound photonic states embedded into
the radiation continuum. We study dielectric metasurfaces composed of planar
periodic arrays of Mie-resonant nanoparticles ("meta-atoms") which support both
symmetry protected and accidental bound states in the continuum and employ the
multipole decomposition approach to reveal the physical mechanism of the
formation of such nonradiating states in terms of multipolar modes generated by
isolated meta-atoms. Based on the symmetry of the vector spherical harmonics,
we identify the conditions for the existence of bound states in the continuum
originating from the symmetries of both the lattice and the unit cell. Using
this formalism we predict that metasurfaces with strongly suppressed spatial
dispersion can support the bound states in the continuum with the wavevectors
forming a line in the reciprocal space. Our results provide a new way of
designing high-quality resonant photonic systems based on the physics of bound
states in the continuum.Comment: 13 pages, 7 figures, 2 table
Homogenization of metasurfaces formed by random resonant particles in periodical lattices
In this paper we suggest a simple analytical method for description of
electromagnetic properties of a geometrically regular two-dimensional
subwavelength arrays (metasurfaces) formed by particles with randomly
fluctuating polarizabilities. Such metasurfaces are of topical importance due
to development of mass-scale bottom-up fabrication methods, for which
fluctuations of the particles sizes, shapes, and/or composition are inevitable.
Understanding and prediction of electromagnetic properties of such random
metasurfaces is a challenge. We propose an analytical homogenization method
applicable for normal wave incidence on particles arrays with dominating
electric dipole responses and validate it with numerical point-dipole modeling
using the supercell approach. We demonstrate that fluctuations of particles
polarizabilities lead to increased diffuse scattering despite the subwavelength
lattice constant of the array. The proposed method can be readily extended to
oblique incidence and particles with both electric and magnetic dipole
resonances.Comment: 10 pages, 5 figure
Trauma-Informed Care PA-S Pilot Program Evaluation
Background
Trauma stimulates the sympathetic nervous system, creates a fight-or-flight response through the hypothalamic-pituitary-adrenal axis, release of cortisol.1 Repeated stress leads to dysregulation of this response, which can lead to altered stress susceptibility and the inability to cope with stress.2 A trauma-informed approach encourages the provision of care to be based on knowledge and understanding of trauma and its widespread implications on patients lives.3
- Rather than asking what is wrong with you, trauma-informed care encourages providers to ask what happened to you? 5https://jdc.jefferson.edu/mspas_capstones/1011/thumbnail.jp
Acoustic Lateral Recoil Force and Stable Lift of Anisotropic Particles
Acoustic forces and torques are of immense importance for manipulation of
particles, in particular in biomedical applications. While such forces and
torques are well understood for small spherical particles with lowest-order
monopole and dipole responses, the higher-order effects for larger anisotropic
particles have not been properly investigated. Here we examine the acoustic
force and torque on an anisotropic (ellipsoid) particle and reveal two novel
phenomena. First, we describe the lateral recoil force, orthogonal to the
direction of the incident wave and determined by the tilted orientation of the
particle. Second, we find conditions for the stable acoustic lift, where the
balanced torque and force produce a stable lateral drift of the tilted
particle. We argue that these phenomena can bring about new functionalities in
acoustic manipulation and sorting of anisotropic particles including biological
objects such as blood cells.Comment: 11 pages, 7 figure
Optical Pulling and Pushing Forces via Bloch Surface Waves
Versatile manipulation of nano- and microobjects underlies the optomechanics
and a variety of its applications in biology, medicine, and lab-on-a-chip
platforms. For flexible tailoring optical forces, as well as for extraordinary
optomechanical effects, additional degrees of freedom should be introduced into
the system. Here, we demonstrate that photonic crystals provide a flexible
platform for nanoparticles optical manipulation due to both Bloch surface waves
(BSWs) and the complex character of the reflection coefficient paving a way for
complex optomechanical interactions control. We demonstrate that appearance of
enhanced pulling and pushing transversal optical forces acting on a single bead
placed above a one-dimensional photonic crystal due to directional excitation
of Bloch surface wave at the photonic crystal interface. Our theoretical
results, which are supported with numerical simulations, demonstrate angle or
wavelength assisted switching between BSW-induced optical pulling and pushing
forces. Easy-to-fabricate for any desired spectral range photonic crystals are
shown to be prospective for precise optical sorting of nanoparticles,
especially for core-shell nanoparticles, which are difficult to sort with
conventional optomechanical methods. Our approach opens opportunities for novel
optical manipulation schemes and platforms and enhanced light-matter
interaction in optical trapping setups
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