278 research outputs found
Ultrafast spectroscopy of single molecules
We present a single-molecule study on femtosecond dynamics in multichromophoric systems, combining fs pump-probe, emission-spectra and fluorescence-lifetime analysis. At the single molecule level a wide range of exciton delocalisation lengths and energy redistribution times is revealed. Next, two color pump-probe experiments are presented as a step to addressing ultrafast energy transfer in individual complexes
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Coupling a single solid-state quantum emitter to an array of resonant plasmonic antennas
Plasmon resonant arrays or meta-surfaces shape both the incoming optical field and the local density of states for emission processes. They provide large regions of enhanced emission from emitters and greater design flexibility than single nanoantennas. This makes them of great interest for engineering optical absorption and emission. Here we study the coupling of a single quantum emitter, a self-assembled semiconductor quantum dot, to a plasmonic meta-surface. We investigate the influence of the spectral properties of the nanoantennas and the position of the emitter in the unit cell of the structure. We observe a resonant enhancement due to emitter-array coupling in the far-field regime and find a clear difference from the interaction of an emitter with a single antenna
Ultrafast time-resolved spectroscopy of 1D metal-dielectric photonic crystals
We study the all-optical switching behavior of one-dimensional
metal-dielectric photonic crystals due to the nonlinearity of the free metal
electrons. A polychromatic pump-probe setup is used to determine the wavelength
and pump intensity dependence of the ultrafast transmission suppression as well
as the dynamics of the process on a subpicosecond timescale. We find ultrafast
(sub-picosecond) as well as a slow (millisecond) behavior. We present a model
of the ultrafast dynamics and nonlinear response which can fit the measured
data well and allows us to separate the thermal and the electronic response of
the system.Comment: 7 pages, 5 figure
Nanoantenna-enhanced ultrafast nonlinear spectroscopy of a single gold nanoparticle
Optical nanoantennas are a novel tool to investigate previously unattainable
dimensions in the nanocosmos. Just like their radio-frequency equivalents,
nanoantennas enhance the light-matter interaction in their feed gap. Antenna
enhancement of small signals promises to open a new regime in linear and
nonlinear spectroscopy on the nanoscale. Without antennas especially the
nonlinear spectroscopy of single nanoobjects is very demanding. Here, we
present for the first time antenna-enhanced ultrafast nonlinear optical
spectroscopy. In particular, we utilize the antenna to determine the nonlinear
transient absorption signal of a single gold nanoparticle caused by mechanical
breathing oscillations. We increase the signal amplitude by an order of
magnitude which is in good agreement with our analytical and numerical models.
Our method will find applications in linear and nonlinear spectroscopy of
nanoobjects, ranging from single protein binding events via nonlinear tensor
elements to the limits of continuum mechanics
molecular recognition at interfaces
In order to investigate molecular recognition on surfaces, an azide-
functionalized monolayer was deposited on gold. The monolayer was
characterized by X-ray photoelectron spectroscopy (XPS) and angle-resolved
near-edge X-ray absorption fine structure (NEXAFS) experiments and the
decomposition of the azide upon irradiation with X-ray beams was investigated.
Subsequently, various alkyne-functionalized host and guest molecules were
attached to the azide by 1,3-dipolar cycloaddition. These modified surfaces
and their host–guest chemistry were analysed by XPS and angle-resolved NEXAFS.
The reversibility of guest binding was shown for one example as a proof of
principle
Full counting statistics of quantum dot resonance fluorescence
The electronic energy levels and optical transitions of a semiconductor quantum dot are subject to dynamics within the solid-state environment. In particular, fluctuating electric fields due to nearby charge traps or other quantum dots shift the transition frequencies via the Stark effect. The environment dynamics are mapped directly onto the fluorescence under resonant excitation and diminish the prospects of quantum dots as sources of indistinguishable photons in optical quantum computing. Here, we present an analysis of resonance fluorescence fluctuations based on photon counting statistics which captures the underlying time-averaged electric field fluctuations of the local environment. The measurement protocol avoids dynamic feedback on the electric environment and the dynamics of the quantum dot's nuclear spin bath by virtue of its resonant nature and by keeping experimental control parameters such as excitation frequency and external fields constant throughout. The method introduced here is experimentally undemanding
A multi-targeted approach to suppress tumor-promoting inflammation
Cancers harbor significant genetic heterogeneity and patterns of relapse following many therapies are due to evolved resistance to treatment. While efforts have been made to combine targeted therapies, significant levels of toxicity have stymied efforts to effectively treat cancer with multi-drug combinations using currently approved therapeutics. We discuss the relationship between tumor-promoting inflammation and cancer as part of a larger effort to develop a broad-spectrum therapeutic approach aimed at a wide range of targets to address this heterogeneity. Specifically, macrophage migration inhibitory factor, cyclooxygenase-2, transcription factor nuclear factor-κB, tumor necrosis factor alpha, inducible nitric oxide synthase, protein kinase B, and CXC chemokines are reviewed as important antiinflammatory targets while curcumin, resveratrol, epigallocatechin gallate, genistein, lycopene, and anthocyanins are reviewed as low-cost, low toxicity means by which these targets might all be reached simultaneously. Future translational work will need to assess the resulting synergies of rationally designed antiinflammatory mixtures (employing low-toxicity constituents), and then combine this with similar approaches targeting the most important pathways across the range of cancer hallmark phenotypes
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