62 research outputs found
Observation of the photorefractive effect in a polymer
We report the first observation of the photorefractive effect in a polymeric material, the electro-optic polymer bisphenol-A-diglycidylether 4-nitro-1,2-phenylenediamine made photoconductive by doping with the hole-transport agent diethylamino-benzaldehyde diphenylhydrazone. The gratings formed exhibit dynamic writing and erasure, strong electric-field dependence, polarization anisotropy, and estimated space-charge fields up to 26 kV/cm at an applied field of 126 kV/cm. Application of similar concepts should provide a broad new class of easily fabricated photorefractive materials
Interferometry of a Single Nanoparticle Using the Gouy Phase of a Focused Laser Beam
We provide a quantitative explanation of the mechanism of the far-field
intensity modulation induced by a nanoparticle in a focused Gaussian laser
beam, as was demonstrated in several recent direct detection studies. Most
approaches take advantage of interference between the incident light and the
scattered light from a nanoparticle to facilitate a linear dependence of the
signal on the nanoparticle volume. The phase relation between the incoming
field and the scattered field by the nanoparticle is elucidated by the concept
of Gouy phase. This phase relation is used to analyze the far-field
signal-to-noise ratio as a function of exact nanoparticle position with respect
to the beam focus. The calculation suggests that a purely dispersive
nanoparticle should be displaced from the Gaussian beam focus to generate a
far-field intensity change
Single-molecule trapping and spectroscopy reveals photophysical heterogeneity of phycobilisomes quenched by Orange Carotenoid Protein
Upon photoactivation the Orange Carotenoid Protein (OCP) binds to the phycobilisome and prevents damage by thermally dissipating excess energy. Here authors use an Anti-Brownian ELectrokinetic trap to determine the photophysics of single OCP-quenched phycobilisomes and observe two distinct OCP-quenched states with either one or two OCPs bound
Strongly focused light beams interacting with single atoms in free space
We construct 3-D solutions of Maxwell's equations that describe Gaussian
light beams focused by a strong lens. We investigate the interaction of such
beams with single atoms in free space and the interplay between angular and
quantum properties of the scattered radiation. We compare the exact results
with those obtained with paraxial light beams and from a standard input-output
formalism. We put our results in the context of quantum information processing
with single atoms.Comment: 9 pages, 9 figure
Single-molecule identification of quenched and unquenched states of LHCII
In photosynthetic light harvesting, absorbed
sunlight is converted to electron flow with near-unity quantum
efficiency under low light conditions. Under high light
conditions, plants avoid damage to their molecular machinery
by activating a set of photoprotective mechanisms to
harmlessly dissipate excess energy as heat. To investigate
these mechanisms, we study the primary antenna complex in
green plants, light-harvesting complex II (LHCII), at the
single-complex level. We use a single-molecule technique, the Anti-Brownian Electrokinetic trap, which enables simultaneous
measurements of fluorescence intensity, lifetime, and spectra in solution. With this approach, including the first measurements of
fluorescence lifetime on single LHCII complexes, we access the intrinsic conformational dynamics. In addition to an unquenched
state, we identify two partially quenched states of LHCII. Our results suggest that there are at least two distinct quenching sites
with different molecular compositions, meaning multiple dissipative pathways in LHCII. Furthermore, one of the quenched
conformations significantly increases in relative population under environmental conditions mimicking high light.This material is based on work supported in part by the U.S. Department of Energy,
Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences,
Geosciences, and Biosciences under Award Number DE-FG02-07ER15892 (to W.E.M)
and by the Dutch organization for scientific research (NWO-ALW) via a Vici grant (to
R.C.). R.v.G. and T.P.J.K. were supported by the Netherlands Organization for Sciences,
Council of Chemical Sciences (NWO-CW) via a TOP-grant (700.58.305). R.v.G. was
further supported by an Advanced Investigator grant from the European Research
Council (no. 267333, PHOTPROT) and by the EU FP7 project PAPETS (GA 323901).
R.v.G. gratefully acknowledges his Academy Professor grant from the Royal Netherlands
Academy of Arts and Sciences (KNAW). T.P.J.K. was further supported by University of
Pretoria’s Research Development Programme (grant no. A0W679). The authors would
like to acknowledge the following fellowships: a Postdoctoral Fellowship from the
Center for Molecular Analysis and Design at Stanford University (to G.S.S.-C.); a
Kenneth and Nina Tai Stanford Graduate Fellowship (to H.-Y.Y.); and a Long Term
Fellowship from EMBO (to M.G.).http://pubs.acs.org/journal/jpclcdhb2017Physic
Single-molecule identification of quenched and unquenched states of LHCII
In photosynthetic light harvesting, absorbed
sunlight is converted to electron flow with near-unity quantum
efficiency under low light conditions. Under high light
conditions, plants avoid damage to their molecular machinery
by activating a set of photoprotective mechanisms to
harmlessly dissipate excess energy as heat. To investigate
these mechanisms, we study the primary antenna complex in
green plants, light-harvesting complex II (LHCII), at the
single-complex level. We use a single-molecule technique, the Anti-Brownian Electrokinetic trap, which enables simultaneous
measurements of fluorescence intensity, lifetime, and spectra in solution. With this approach, including the first measurements of
fluorescence lifetime on single LHCII complexes, we access the intrinsic conformational dynamics. In addition to an unquenched
state, we identify two partially quenched states of LHCII. Our results suggest that there are at least two distinct quenching sites
with different molecular compositions, meaning multiple dissipative pathways in LHCII. Furthermore, one of the quenched
conformations significantly increases in relative population under environmental conditions mimicking high light.This material is based on work supported in part by the U.S. Department of Energy,
Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences,
Geosciences, and Biosciences under Award Number DE-FG02-07ER15892 (to W.E.M)
and by the Dutch organization for scientific research (NWO-ALW) via a Vici grant (to
R.C.). R.v.G. and T.P.J.K. were supported by the Netherlands Organization for Sciences,
Council of Chemical Sciences (NWO-CW) via a TOP-grant (700.58.305). R.v.G. was
further supported by an Advanced Investigator grant from the European Research
Council (no. 267333, PHOTPROT) and by the EU FP7 project PAPETS (GA 323901).
R.v.G. gratefully acknowledges his Academy Professor grant from the Royal Netherlands
Academy of Arts and Sciences (KNAW). T.P.J.K. was further supported by University of
Pretoria’s Research Development Programme (grant no. A0W679). The authors would
like to acknowledge the following fellowships: a Postdoctoral Fellowship from the
Center for Molecular Analysis and Design at Stanford University (to G.S.S.-C.); a
Kenneth and Nina Tai Stanford Graduate Fellowship (to H.-Y.Y.); and a Long Term
Fellowship from EMBO (to M.G.).http://pubs.acs.org/journal/jpclcdhb2017Physic
Photon Statistics; Nonlinear Spectroscopy of Single Quantum Systems
A unified description of multitime correlation functions, nonlinear response
functions, and quantum measurements is developed using a common generating
function which allows a direct comparison of their information content. A
general formal expression for photon counting statistics from single quantum
objects is derived in terms of Liouville space correlation functions of the
material system by making a single assumption that spontaneous emission is
described by a master equation
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