254 research outputs found
Tailoring correlations of the local density of states in disordered photonic materials
We present experimental evidence for the different mechanisms driving the
fluctuations of the local density of states (LDOS) in disordered photonic
systems. We establish a clear link between the microscopic structure of the
material and the frequency correlation function of LDOS accessed by a
near-field hyperspectral imaging technique. We show, in particular, that short-
and long-range frequency correlations of LDOS are controlled by different
physical processes (multiple or single scattering processes, respectively) that
can be---to some extent---manipulated independently. We also demonstrate that
the single scattering contribution to LDOS fluctuations is sensitive to
subwavelength features of the material and, in particular, to the correlation
length of its dielectric function. Our work paves a way towards a complete
control of statistical properties of disordered photonic systems, allowing for
designing materials with predefined correlations of LDOS.Comment: 5+9 pages, 5+6 figures. Fixed confusion of references between the
main text and the supplemental material in version
Revealing single emitter spectral dynamics from intensity correlations in an ensemble fluorescence spectrum
We show that the single emitter linewidth underlying a broadened ensemble
emission spectrum can be extracted from correlations among the stochastic
intensity fluctuations in the ensemble spectrum. Spectral correlations can be
observed at high temporal and spectral resolutions with a cross-correlated pair
of avalanche photodiodes placed at the outputs of a scanning Michelson
interferometer. As illustrated with simulations in conjunction with
Fluorescence Correlation Spectroscopy, our approach overcomes ensemble and
temporal inhomogeneous broadening to provide single emitter linewidths, even
for emitters under weak, continuous, broadband excitation.Comment: 9 pages, 5 figure
Temperature-dependent near-field imaging of delocalized and localized excitons in single quantum wires
Summary form only given. Recent microphotoluminescence studies have shown that the low-temperature emission spectra of semiconductor quantum wires are dominated by localized, quasi-zero-dimensional, excitons. This implies that both the optical and transport properties of such quasi-one-dimensional (Q1D) nanostructures are similar to that of a chain of quantum dots. It also hinders the observation of some truly one-dimensional quantum effects, such as the ballistic or diffusive one-dimensional exciton transport, expected in nanostructures containing Q1D excitons that are delocalized over mesoscopic length scales. We present the first experimental evidence for such delocalized excitons in a single quantum wire. A novel coupled quantum wire-dot nanostructure is studied by low temperature near-field photoluminescence (PL) spectroscopy
Multimode photonic molecules for advanced force sensing
We propose a force sensor, with optical detection, based on a reconfigurable multicavity photonic molecule distributed over two parallel photonic crystal membranes. The system spectral behaviour is described with an analytical model based on coupled mode theory and validated by finite difference time domain simulations. The deformation of the upper photonic crystal membrane, due to a localized vertical force, is monitored by the relative spectral positions of the photonic molecule resonances. The proposed system can act both as force sensor, with pico-newton sensitivity, able to identify the position where the force is applied, and as torque sensor able to measure the torsion of the membrane along two perpendicular directions
Near-field optical imaging and spectroscopy of a coupled quantum wire-dot structure
A coupled GaAs/AlGaAs quantum wire (QWR)-dot sample grown by molecular beam epitaxy on a patterned (311)A GaAs substrate is studied by near-field spectroscopy at a temperature of 10 K with a spectral resolution of 100 µeV. The two-dimensional potential energy profiles of the sample including localized excitonic states caused by structural disorder are determined in photoluminescence measurements with a spatial resolution of 150 nm. One finds a potential barrier of 20 meV between the quantum wire and the embedding quantum well (QW) on the mesa top of the structure. This is due to local thinning of the GaAs layer. In contrast, the wire-dot interface results free of energy barriers. The spatial variation of the GaAs layer thickness provides information on the growth mechanism determined by lateral diffusion of Ga atoms which is modeled by an analytical model. By performing spatially resolved photoluminescence excitation measurements on this wire-dot structure, we present a method for investigating carrier transport in low-dimensional systems: The dot area is used as an optical marker for excitonic diffusion via QW and QWR states. The two-dimensional (2D) and 1D diffusion coefficients are extracted as a function of the temperature and discussed
Near-field distribution and propagation of scattering resonances in Vogel spiral arrays of dielectric nanopillars
In this work, we employ scanning near-field optical microscopy, full-vector finite difference time domain numerical simulations and fractional Fourier transformation to investigate the near-field and propagation behavior of the electromagnetic energy scattered at 1.56µm by dielectric arrays of silicon nitride nanopillars with chiral 1-Vogel spiral geometry. In particular, we experimentally study the spatial evolution of scattered radiation and demonstrate near-field coupling between adjacent nanopillars along the parastichies arms. Moreover, by measuring the spatial distribution of the scattered radiation at different heights from the array plane, we demonstrate a characteristic rotation of the scattered field pattern consistent with net transfer of orbital angular momentum in the Fresnel zone, within a few micrometers from the plane of the array. Our experimental results agree with the simulations we performed and may be of interest to nanophotonics applications
Superlinear emission in bare perovskite: amplified spontaneous emission in disordered film versus single crystal lasing
Abstract We present an experimental study concerning the superlinear emission in organic-inorganic halide perovskites. Microphotoluminescence experiments under CW and picosecond excitation condition at low temperature and near field optical photoluminescence spectra at room temperature provide clear evidence of the very different origin of the superlinear regime in disordered films and microplates/microwires. Insights on the origin of modal structures of the emission spectra in the high excitation regime will be given by polarization-resolved photoluminescence experiments
Post-fabrication control of evanescent tunnelling in photonic crystal molecules
The post-fabrication control of evanescent tunnelling in photonic crystal molecules is demonstrated through the combination of selective infiltration and oxidation. By laser non thermal oxidation, we reduce the photonic coupling by more than 30% while by means of water micro-infiltration, we increase it by 28%. Fine-tuning of the photonic coupling is achieved by low-power laser oxidation and forced evaporation, opening the route to post-fabrication control of array of coupled cavities
Near-field imaging of single walled carbon nanotubes emitting in the telecom wavelength range
International audienceHybrid systems based on carbon nanotubes emitting in the telecom wavelength range and Si-photonic platforms are promising candidates for developing integrated photonic circuits. Here, we consider semiconducting single walled carbon nanotubes (s-SWNTs) emitting around 1300 nm or 1550 nm wavelength. The nanotubes are deposited on quartz substrate for mapping their photoluminescence in hyperspectral near-field microscopy. This method allows for a sub-wavelength resolution in detecting the spatial distribution of the emission of single s-SWNTs at room temperature. Optical signature delocalized over several micrometers is observed, thus denoting the high quality of the produced carbon nanotubes on a wide range of tube diameters. Noteworthy, the presence of both nanotube bundles and distinct s-SWNT chiralities is uncovered
Nonlinear optical tuning of photonic crystal microcavities by near-field probe
We report on a nonlinear way to control and tune the dielectric environment of photonic crystalmicrocavities exploiting the local heating induced by near-field laser excitation at differentexcitation powers. The temperature gradient due to the optical absorption results in an index ofrefraction gradient which modifies the dielectric surroundings of the cavity and shifts the opticalmodes. Reversible tuning can be obtained either by changing the excitation power density or byexciting in different points of the photonic crystal microcavity
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