177 research outputs found
Optical-fiber-microsphere for remote fluorescence correlation spectroscopy
International audienceFluorescence correlation spectroscopy (FCS) is a versatile method that would greatly benefit to remote optical-fiber fluorescence sensors. However, the current state-of-the-art struggles with high background and low detection sensitivities that prevent the extension of fiber-based FCS down to the single-molecule level. Here we report the use of an optical fiber combined with a latex microsphere to perform FCS analysis. The sensitivity of the technique is demonstrated at the single molecule level thanks to a photonic nanojet effect. This offers new opportunities for reducing the bulky microscope setup and extending FCS to remote or in vivo applications
Signatures of exciton coupling in paired nanoemitters
An exciton formed by the delocalized electronic excitation of paired nanoemitters is interpreted in terms of the electromagnetic emission of the pair and their mutual coupling with a photodetector. A formulation directly tailored for fluorescence detection is identified, giving results which are strongly dependent on geometry and selection rules. Signature symmetric and antisymmetric combinations are analyzed and their distinctive features identified
Ionization degree of the electron-hole plasma in semiconductor quantum wells
The degree of ionization of a nondegenerate two-dimensional electron-hole
plasma is calculated using the modified law of mass action, which takes into
account all bound and unbound states in a screened Coulomb potential.
Application of the variable phase method to this potential allows us to treat
scattering and bound states on the same footing. Inclusion of the scattering
states leads to a strong deviation from the standard law of mass action. A
qualitative difference between mid- and wide-gap semiconductors is
demonstrated. For wide-gap semiconductors at room temperature, when the bare
exciton binding energy is of the order of T, the equilibrium consists of an
almost equal mixture of correlated electron-hole pairs and uncorrelated free
carriers.Comment: 22 pages, 6 figure
Mode-matching in multiresonant plasmonic nanoantennas for enhanced second harmonic generation
Boosting nonlinear frequency conversion in extremely confined volumes remains
a key challenge in nano-optics, nanomedicine, photocatalysis, and
background-free biosensing. To this aim, field enhancements in plasmonic
nanostructures are often exploited to effectively compensate for the lack of
phase-matching at the nanoscale. Second harmonic generation (SHG) is, however,
strongly quenched by the high degree of symmetry in plasmonic materials at the
atomic scale and in nanoantenna designs. Here, we devise a plasmonic
nanoantenna lacking axial symmetry, which exhibits spatial and frequency mode
overlap at both the excitation and the SHG wavelengths. The effective
combination of these features in a single device allows obtaining unprecedented
SHG conversion efficiency. Our results shed new light on the optimization of
SHG at the nanoscale, paving the way to new classes of nanoscale coherent light
sources and molecular sensing devices based on nonlinear plasmonic platforms.Comment: 14 pages, 4 figure
Mode imaging and selection in strongly coupled nanoantennas
The number of eigenmodes in plasmonic nanostructures increases with
complexity due to mode hybridization, raising the need for efficient mode
characterization and selection. Here we experimentally demonstrate direct
imaging and selective excitation of the bonding and antibonding plasmon mode in
symmetric dipole nanoantennas using confocal two-photon photoluminescence
mapping. Excitation of a high-quality-factor antibonding resonance manifests
itself as a two-lobed pattern instead of the single spot observed for the broad
bonding resonance, in accordance with numerical simulations. The two-lobed
pattern is observed due to the fact that excitation of the antibonding mode is
forbidden for symmetric excitation at the feedgap, while concomitantly the mode
energy splitting is large enough to suppress excitation of the bonding mode.
The controlled excitation of modes in strongly coupled plasmonic nanostructures
is mandatory for efficient sensors, in coherent control as well as for
implementing well-defined functionalities in complex plasmonic devices.Comment: 11 pages, 5 figures, 1 supplementary informatio
Angle-Tunable Enhanced Infrared Reflection Absorption Spectroscopy via Grating-Coupled Surface Plasmon Resonance
Surface enhanced infrared absorption (SEIRA) spectroscopy is an attractive method for increasing the prominence of vibrational modes in infrared spectroscopy. To date, the majority of reports associated with SEIRA utilize localized surface plasmon resonance from metal nanoparticles to enhance electromagnetic fields in the region of analytes. Limited work has been performed using propagating surface plasmons as a method for SEIRA excitation. In this report, we demonstrate angle-tunable enhancement of vibrational stretching modes associated with a thin poly(methyl methacrylate) (PMMA) film that is coupled to a silver-coated diffraction grating. Gratings are fabricated using laser interference lithography to achieve precise surface periodicities, which can be used to generate surface plasmons that overlap with specific vibrational modes in the polymer film. Infrared reflection absorption spectra are presented for both bare silver and PMMA-coated silver gratings at a range of angles and polarization states. In addition, spectra were obtained with the grating direction oriented perpendicular and parallel to the infrared source in order to isolate plasmon enhancement effects. Optical simulations using the rigorous coupled-wave analysis method were used to identify the origin of the plasmon-induced enhancement. Angle-dependent absorption measurements achieved signal enhancements of more than 10-times the signal in the absence of the plasmon.This article is from Analytical Chemistry86 (2014): 2610-2617, doi:10.1021/ac4038398. Posted with permission.</p
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