391 research outputs found
Microscopic measurement of photon echo formation in groups of individual excitonic transitions
The third-order polarization emitted from groups of individual localized
excitonic transitions after pulsed optical excitation is measured. We observe
the evolution of the nonlinear response from the case of a free polarization
decay for a single transition, to that of a photon echo for many transitions.
The echo is shown to arise from the mutual rephasing of the emission from
individual transitions
Femtosecond phase-resolved microscopy of plasmon dynamics in individual gold nanospheres
The selective optical detection of individual metallic nanoparticles (NPs)
with high spatial and temporal resolution is a challenging endeavour, yet is
key to the understanding of their optical response and their exploitation in
applications from miniaturised optoelectronics and sensors to medical
diagnostics and therapeutics. However, only few reports on ultrafast pump-probe
spectroscopy on single small metallic NPs are available to date. Here, we
demonstrate a novel phase-sensitive four-wave mixing (FWM) microscopy in
heterodyne detection to resolve for the first time the ultrafast changes of
real and imaginary part of the dielectric function of single small (<40nm)
spherical gold NPs. The results are quantitatively described via the transient
electron temperature and density in gold considering both intraband and
interband transitions at the surface plasmon resonance. This novel microscopy
technique enables background-free detection of the complex susceptibility
change even in highly scattering environments and can be readily applied to any
metal nanostructure
Polarization-resolved extinction and scattering cross-section of individual gold nanoparticles measured by wide-field microscopy on a large ensemble
We report a simple, rapid, and quantitative wide-field technique to measure
the optical extinction and scattering
cross-section of single nanoparticles using wide-field microscopy enabling
simultaneous acquisition of hundreds of nanoparticles for statistical analysis.
As a proof of principle, we measured nominally spherical gold nanoparticles of
40\,nm and 100\,nm diameter and found mean values and standard deviations of
and consistent with previous literature.
Switching from unpolarized to linearly polarized excitation, we measured
as a function of the polarization direction, and used it to
characterize the asphericity of the nanoparticles. The method can be
implemented cost-effectively on any conventional wide-field microscope and is
applicable to any nanoparticles
Realistic heterointerfaces model for excitonic states in growth-interrupted quantum wells
We present a model for the disorder of the heterointerfaces in GaAs quantum
wells including long-range components like monolayer island formation induced
by the surface diffusion during the epitaxial growth process. Taking into
account both interfaces, a disorder potential for the exciton motion in the
quantum well plane is derived. The excitonic optical properties are calculated
using either a time-propagation of the excitonic polarization with a
phenomenological dephasing, or a full exciton eigenstate model including
microscopic radiative decay and phonon scattering rates. While the results of
the two methods are generally similar, the eigenstate model does predict a
distribution of dephasing rates and a somewhat modified spectral response.
Comparing the results with measured absorption and resonant Rayleigh scattering
in GaAs/AlAs quantum wells subjected to growth interrupts, their specific
disorder parameters like correlation lengths and interface flatness are
determined. We find that the long-range disorder in the two heterointerfaces is
highly correlated, having rather similar average in-plane correlation lengths
of about 60 and 90 nm. The distribution of dephasing rates observed in the
experiment is in agreement with the results of the eigenstate model. Finally,
we simulate highly spatially resolved optical experiments resolving individual
exciton states in the deduced interface structure.Comment: To appear in Physical Review
Optimizing the Drude-Lorentz model for material permittivity: Examples for semiconductors
Approximating the frequency dispersion of the permittivity of materials with
simple analytical functions is of fundamental importance for understanding and
modeling their optical properties. Quite generally, the permittivity can be
treated in the complex frequency plane as an analytic function having a
countable number of simple poles which determine the dispersion of the
permittivity, with the pole weights corresponding to generalized conductivities
of the medium at these resonances. The resulting Drude-Lorentz model separates
the poles at frequencies with zero real part (Ohm's law and Drude poles) from
poles with finite real part (Lorentz poles). To find the parameters of such an
analytic function, we minimize the error weighted deviation between the model
and measured values of the permittivity. We show examples of such optimizations
for various semiconductors (Si, GaAs and Ge), for different frequency ranges
and up to five pairs of Lorentz poles accounted for in the model.Comment: arXiv admin note: substantial text overlap with arXiv:1612.0692
Comment on "normalization of quasinormal modes in leaky optical cavities and plasmonic resonators"
Recently, Kristensen, Ge and Hughes have compared [Phys. Rev. A 92, 053810 (2015)] three
di�erent methods for normalization of quasinormal modes in open optical systems, and concluded
that they all provide the same result. We show here that this conclusion is incorrect and illustrate
that the normalization of [Opt. Lett. 37, 1649 (2012)] is divergent for any optical mode having a
�nite quality factor, and that the Silver-M�uller radiation condition is not ful�lled for quasinormal
modes
Polariton states bound to defects in GaAs/AlAs planar microcavities
We report on polariton states bound to defects in planar GaAs/AlAs
microcavities grown by molecular beam epitaxy. The defect types relevant for
the spatial polariton dynamics in these structures are cross-hatch misfit
dislocations, and point-like defects extended over several micrometers. We
attribute the latter defects to Ga droplets emitted occasionally by the Ga cell
during the growth. These defects, also known as oval defects, result in a
dome-like local modulation of surface, which is translated into the cavity
structure and leads to a lateral modulation of the cavity polariton energy of
up to 15\,meV. The resulting spatially localized potential landscape for the
in-plane polariton motion creates a series of bound states. These states were
characterized by spectrally resolved transmission imaging in real and
reciprocal space, and reveal the spatial potential created by the defects.
Interestingly, the defect states exhibit long lifetimes in the 10ps range,
which we attribute to a spatially smooth confinement potential
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