557 research outputs found
Stimulated Raman Adiabatic Passage (STIRAP) as a Route to Achieving Optical Control in Plasmonics
Optical properties of ensembles of three-level quantum emitters coupled to
plasmonic systems are investigated employing a self-consistent model. It is
shown that stimulated Raman adiabatic passage (STIRAP) technique can be
successfully adopted to control optical properties of hybrid materials with
collective effects present and playing an important role in light-matter
interactions. We consider a core-shell nanowire comprised of a silver core and
a shell of coupled quantum emitters and utilize STIRAP scheme to control
scattering efficiency of such a system in a frequency and spatial dependent
manner. After the STIRAP induced population transfer to the final state takes
place, the core-shell nanowire exhibits two sets of Rabi splittings with Fano
lineshapes indicating strong interactions between two different atomic
transitions driven by plasmon near-fields.Comment: 11 pages, 6 figures, accepted, Physical Review
Hydrophobic gating of mechanosensitive channel of large conductance evidenced by single-subunit resolution
Mechanosensitive (MS) ion channels are membrane proteins that detect and respond to membrane tension in all branches of life. In bacteria, MS channels prevent cells from lysing upon sudden hypoosmotic shock by opening and releasing solutes and water. Despite the importance of MS channels and ongoing efforts to explain their functioning, the molecular mechanism of MS channel gating remains elusive and controversial. Here we report a method that allows single-subunit resolution for manipulating and monitoring “mechanosensitive channel of large conductance” from Escherichia coli. We gradually changed the hydrophobicity of the pore constriction in this homopentameric protein by modifying a critical pore residue one subunit at a time. Our experimental results suggest that both channel opening and closing are initiated by the transmembrane 1 helix of a single subunit and that the participation of each of the five identical subunits in the structural transitions between the closed and open states is asymmetrical. Such a minimal change in the pore environment seems ideal for a fast and energy-efficient response to changes in the membrane tension.
Perfect coupling of light to surface plasmons with ultra-narrow linewidths
We examine the coupling of electromagnetic waves incident normal to a thin
silver film that forms an oscillatory grating embedded between two otherwise
uniform, semi-infinite half spaces. Two grating structures are considered, in
one of which the mid point of the Ag film remains fixed whereas the thickness
varies sinusoidally, while in the other the mid point oscillates sinusoidally
whereas the film thicknesses remains fixed. On reducing the light wavelength
from the long wavelength limit, we encounter signatures in the transmission, T,
and reflection, R, coefficients associated with: i) the short-range surface
plasmon mode, ii) the long-range surface plasmon mode, and iii) electromagnetic
diffraction tangent to the grating. The first two features can be regarded as
generalized (plasmon) Wood's anomalies whereas the third is the first-order
conventional (electromagnetic) Wood's anomaly. The energy density at the film
surface is enhanced for wavelengths corresponding to these three anomalies,
particularly for the long range plasmon mode in thin films. When exciting the
silver film with a pair of waves incident from opposite directions, we find
that by adjusting the grating oscillation amplitude and fixing the relative
phase of the incoming waves to be even or odd, T+R can be made to vanish for
one or the other of the plasmon modes; this corresponds to perfect coupling
(impedance matching in the language of electrical engineering) between the
incoming light and these modes.Comment: 13 pages, 5 figures. accepted J. Chem. Phy
Gating-by-tilt of mechanosensitive membrane channels
We propose an alternative mechanism for the gating of biological membrane
channels in response to membrane tension that involves a change in the slope of
the membrane near the channel. Under biological membrane tensions we show that
the energy difference between the closed (tilted) and open (untilted) states
can far exceed kBT and is comparable to what is available under simple
ilational gating. Recent experiments demonstrate that membrane leaflet
asymmetries (spontaneous curvature) can strong effect the gating of some
channels. Such a phenomenon would be more easy to explain under gating-by-tilt,
given its novel intrinsic sensitivity to such asymmetry.Comment: 10 pages, 2 figure
Light trapping and guidance in plasmonic nanocrystals
We illustrate the possibility of light trapping and funneling in periodic
arrays of metallic nanoparticles. A controllable minimum in the transmission
spectra of such constructs arises from a collective plasmon resonance
phenomenon, where an incident plane wave sharply localizes in the vertical
direction, remaining delocalized in the direction parallel to the crystal
plane. Using hybrid arrays of different structures or different materials, we
apply the trapping effect to structure the eigen-mode spectrum, introduce
overlapping resonances, and hence direct the light in space in a
wavelength-sensitive fashion
Optimal design of nanoplasmonic materials using genetic algorithms as a multi-parameter optimization tool
An optimal control approach based on multiple parameter genetic algorithms is
applied to the design of plasmonic nanoconstructs with pre-determined optical
properties and functionalities. We first develop nanoscale metallic lenses that
focus an incident plane wave onto a pre-specified, spatially confined spot. Our
results illustrate the role of symmetry breaking and unravel the principles
that favor dimeric constructs for optimal light localization. Next we design a
periodic array of silver particles to modify the polarization of an incident,
linearly-polarized plane wave in a desired fashion while localizing the light
in space. The results provide insight into the structural features that
determine the birefringence properties of metal nanoparticles and their arrays.
Of the variety of potential applications that may be envisioned, we note the
design of nanoscale light sources with controllable coherence and polarization
properties that could serve for coherent control of molecular or electronic
dynamics in the nanoscale.Comment: 13 pages, 6 figures. submitted to J. Chem. Phy
Coupling, lifetimes and "strong coupling" maps for single molecules at plasmonic interfaces
The interaction between excited states of a molecule and excited states of
metal nanostructure (e.g. plasmons) leads to hybrid states with modified
optical properties. When plasmon resonance is swept through molecular
transition frequency an avoided crossing may be observed, which is often
regarded as a signature of strong coupling between plasmons and molecules. Such
strong coupling is expected to be realized when , where
and are the molecule-plasmon coupling and the spectral width of
the optical transition respectively. Because both and strongly
increase with decreasing distance between a molecule and a plasmonic structure
it is not obvious that this condition can be satisfied for any molecule-metal
surface distance. In this work we investigate the behavior of and
for several geometries. Surprisingly, we find that if the only
contributions to are lifetime broadenings associated with the
radiative and nonradiative relaxation of a single molecular vibronic
transition, including effects on molecular radiative and nonradiative lifetimes
induced by the metal, the criterion is easily satisfied
by many configurations irrespective of the metal-molecule distance. This
implies that the Rabi splitting can be observed in such structures if other
sources of broadening are suppressed. Additionally, when the molecule-metal
surface distance is varied keeping all other molecular and metal parameters
constant, this behavior is mitigated due to the spectral shift associated with
the same molecule-plasmon interaction, making the observation of Rabi splitting
more challenging
О Модернизации Жилищного Законодательства И Построении Эффективных Финансовых Моделей Управления Многоквартирными Домами В Современной России
The article substantiates a set of proposals for amending housing legislation aimed at building effective financial models of various ways to manage apartment buildings in modern Russia. The implementation of the proposals will allow the creation of financially sustainable management organizations in the housing and utilities sector, who receive their remuneration in legal form and are interested in the results of their financial and economic activities. The study was carried out with the financial support of the Russian Foundation for Basic Research in the framework of the research project No. 18-010-00090 “Study of the financial and economic aspects of the activities of management companies in the housing and utilities sector and the development of proposals to improve their financial sustainability.”El artículo respalda un conjunto de propuestas para enmendar la legislación de vivienda con el objetivo de construir modelos financieros efectivos de varias maneras de administrar edificios de apartamentos en la Rusia moderna. La implementación de las propuestas permitirá la creación de organizaciones de gestión financieramente sostenibles en el sector de vivienda y servicios públicos, que reciben su remuneración en forma legal y están interesados en los resultados de sus actividades financieras y económicas. El estudio se realizó con el apoyo financiero de la Fundación Rusa para la Investigación Básica en el marco del proyecto de investigación Nº 18-010-00090 "Estudio de los aspectos financieros y económicos de las actividades de las empresas de gestión en el sector de la vivienda y los servicios públicos. y el desarrollo de propuestas para mejorar su sostenibilidad financiera ". В статье обосновывается комплекс предложений по изменению жилищного законодательства, направленного на построение эффективных финансовых моделей различных способов управления многоквартирными домами в современной России. Реализация предложений позволит создать финансово устойчивые управляющие организации сферы ЖКХ, получающие свое вознаграждение в легальной форме и заинтересованные в результатах своей финансово-хозяйственной деятельности. Исследование выполнено при финансовой поддержке Российского фонда фундаментальных исследований в рамках научного проекта № 18-010-00090 «Исследование финансово-экономических аспектов деятельности управляющих компаний в сфере ЖКХ и разработка предложений по повышению их финансовой устойчивости»
Transport and optical response of molecular junctions driven by surface plasmon-polaritons
We consider a biased molecular junction subjected to external time-dependent
electromagnetic field. The field for two typical junction geometries (bowtie
antennas and metal nanospheres) is calculated within finite-difference
time-domain technique. Time-dependent transport and optical response of the
junctions is calculated within non-equilibrium Green's function approach
expressed in a form convenient for description of multi-level systems. We
present numerical results for a two-level (HOMO-LUMO) model, and discuss
influence of localized surface plasmon polariton modes on transport.Comment: 9 pages, 6 figure
Optical properties of metal nanoparticles with no center of inversion symmetry: observation of volume plasmons
We present theoretical and experimental studies of the optical response of
L-shaped silver nanoparticles. The scattering spectrum exhibits several plasmon
resonances that depend sensitively on the polarization of the incident
electromagnetic field. The physical origin of the resonances is traced to
different plasmon phenomena. In particular, a high energy band with unusual
properties is interpreted in terms of volume plasmon oscillations arising from
the asymmetry of a nanoparticle.Comment: 14 pages, 5 figures. Physical Review B, 2007, accepte
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