200 research outputs found
Light Engineering of the Polariton Landscape in Semiconductor Microcavities
We demonstrate a method to create potential barriers with polarized light
beams for polaritons in semiconductor microcavities. The form of the barriers
is engineered via the real space shape of a focalised beam on the sample. Their
height can be determined by the visibility of the scattering waves generated in
a polariton fluid interacting with them. This technique opens up the way to the
creation of dynamical potentials and defects of any shape in semiconductor
microcavities.Comment: 4 pages, 5 figure
Spin rings in bi-stable planar semiconductor microcavities
A unique feature of exciton-polaritons, inherited from their mixed
light-matter origin, is the strongly spin-dependent polariton-polariton
interaction, which has been predicted to result in the formation of spin rings
in real space [Shelykh et al., Phys. Rev. Lett. 100, 116401 (2008)]. Here we
experimentally demonstrate the spin bi-stability of exciton-polaritons in an
InGaAs-based semiconductor microcavity under resonant optical pumping. We
observe the formation of spin rings whose size can be finely controlled in a
spatial scale down to the micrometer range, much smaller than the spot size. We
additionally evaluate the sign and magnitude of the antiparallel polariton spin
interaction constant.Comment: 5 pages, 4 figure
Anisotropic Optical Spin Hall Effect in Semiconductor Microcavities
Propagating, directionally dependent, polarized spin-currents are created in
an anisotropic planar semiconductor microcavity, via Rayleigh scattering of
optically injected polaritons in the optical spin Hall regime. The influence of
anisotropy results in the suppression or enhancement of the pseudospin
precession of polaritons scattered into different directions. This is exploited
to create intense spin currents by excitation on top of localized defects. A
theoretical model considering the influence of the total effective magnetic
field on the polariton pseudospin quantitatively reproduces the experimental
observations.Comment: 4 pages, 4 figure
Polarization bistability and resultant spin rings in semiconductor microcavities
The transmission of a pump laser resonant with the lower polariton branch of
a semiconductor microcavity is shown to be highly dependent on the degree of
circular polarization of the pump. Spin dependent anisotropy of
polariton-polariton interactions allows the internal polarization to be
controlled by varying the pump power. The formation of spatial patterns, spin
rings with high degree of circular polarization, arising as a result of
polarization bistability, is observed. A phenomenological model based on spin
dependent Gross-Pitaevskii equations provides a good description of the
experimental results. Inclusion of interactions with the incoherent exciton
reservoir, which provides spin-independent blueshifts of the polariton modes,
is found to be essential.Comment: 5 pages, 3 figure
Motion of spin polariton bullets in semiconductor microcavities
The dynamics of optical switching in semiconductor microcavities in the strong coupling regime is studied by using time- and spatially resolved spectroscopy. The switching is triggered by polarized short pulses which create spin bullets of high polariton density. The spin packets travel with speeds of the order of 106 m/s due to the ballistic propagation and drift of exciton polaritons from high to low density areas. The speed is controlled by the angle of incidence of the excitation beams, which changes the polariton group velocityWe thank R. Houdré for the microcavity sample. This work was supported by the IFRAF, the Agence Nationale pour la Recherche, the Spanish MEC (MAT2008-01555 and QOIT-CSD2006-00019), CAM (S-2009/ESP-1503) and FP7 ITN’s ‘‘Clermont4’’ (235114), and Spin-optronics (237252). We acknowledge the Institut Universitaire de Franc
Discriminant Analysis of Geographical Origin of Cork Planks and Stoppers by Near Infrared Spectroscopy
The objective of this study was to assess the potential of visible and near infrared spectroscopy (VIS+NIRS) combined with multivariate analysis for identifying the geographical origin of cork. The study was carried out on cork planks and natural cork stoppers from the most representative cork-producing areas in the world. Two training sets of international and national cork planks were studied. The first set comprised a total of 479 samples from Morocco, Portugal, and Spain, while the second set comprised a total of 179 samples from the Spanish regions of Andalusia, Catalonia, and Extremadura. A training set of 90 cork stoppers from Andalusia and Catalonia was also studied. Original spectroscopic data were obtained for the transverse sections of the cork planks and for the body and top of the cork stoppers by means of a 6500 Foss-NIRSystems SY II spectrophotometer using a fiber optic probe. Remote reflectance was employed in the wavelength range of 400 to 2500 nm. After analyzing the spectroscopic data, discriminant models were obtained by means of partial least square (PLS) with 70% of the samples. The best models were then validated using 30% of the remaining samples. At least 98% of the international cork plank samples and 95% of the national samples were correctly classified in the calibration and validation stage. The best model for the cork stoppers was obtained for the top of the stoppers, with at least 90% of the samples being correctly classified. The results demonstrate the potential of VIS + NIRS technology as a rapid and accurate method for predicting the geographical origin of cork plank and stopper
Excitonpolariton spin switches
Integrated switching devices comprise the building blocks of ultrafast optical signal processing The development of integrated optoelectronic devices relies on three fundamental elements: switching, transport and low-level logic (AND, OR and so on) Optoelectronic devices based on excitons partially solve the problem of integrability, and transistor operation 15 , switching Exciton-polaritons combine the best features of photonic and excitonic systems, demonstrating a qualitative improvement in terms of scalability, reduced power of operation, speed and potential use in logic devices. Polaritons are mixed light-matter quasiparticles that arise from the strong coupling between photons and excitons in a micrometre-sized cavity with embedded quantum wells. Their very low mass ( 10 24 times that of the electron, inherited from their photonic component) enables their propagation over long distances at very high speeds ( 1% the speed of light, on the order of 122 mm ps 21 ), with a controlled direction determined by the momentum of the excitation laser The principle of operation of polariton spin switches is as follows. The system is pumped by an external continuous-wave (c.w.) laser at low power, the wavelength of which is slightly bluedetuned from the energy of a given polariton state in the lower polariton branch (see inset in The emission curve depicted in The rapid polariton motion allows for the switches to be nonloca
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