Detection of the ultranarrow temporal correlation of twin beams via sum-frequency generation

We demonstrate the ultranarrow temporal correlation (6 fs full width half maximum) of twin beams generated by parametric down-conversion, by using the inverse process of sum-frequency generation. The result relies on an achromatic imaging of a huge bandwith of twin beams and on a careful control of their spatial degrees of freedom. The detrimental effects of spatial filtering and of imperfect imaging are shown toghether with the theoretical model used to describe the results

Orbital periods of the binary sdB stars PG0940+068 and PG1247+554

We have used the radial velocity variations of two sdB stars previously reported to be binaries to establish their orbital periods. They are PG0940+068, (P=8.33d) and PG1247+554 (P=0.599d). The minimum masses of the unseen companions, assuming a mass of 0.5 solar masses for the sdB stars, are 0.090 +/- 0.003 solar masses for PG1247+554 and 0.63 +/- 0.02 solar masses for PG0940+068. The nature of the companions is not constrained further by our data.Comment: 5 pages, 2 figure

Normalized ghost imaging

We present an experimental comparison between different iterative ghost imaging algorithms. Our experimental setup utilizes a spatial light modulator for generating known random light fields to illuminate a partially-transmissive object. We adapt the weighting factor used in the traditional ghost imaging algorithm to account for changes in the efficiency of the generated light field. We show that our normalized weighting algorithm can match the performance of differential ghost imaging

Fast full-color computational imaging with single-pixel detectors

Single-pixel detectors can be used as imaging devices by making use of structured illumination. These systems work by correlating a changing incident light field with signals measured on a photodiode to derive an image of an object. In this work we demonstrate a system that utilizes a digital light projector to illuminate a scene with approximately 1300 different light patterns every second and correlate these with the back scattered light measured by three spectrally-filtered single-pixel photodetectors to produce a full-color high-quality image in a few seconds of data acquisition. We utilize a differential light projection method to self normalize the measured signals, improving the reconstruction quality whilst making the system robust to external sources of noise. This technique can readily be extended for imaging applications at non-visible wavebands

Electronic properties of molecular solids: the peculiar case of solid Picene

Recently, a new organic superconductor, K-intercalated Picene with high transition temperatures $T_c$ (up to 18\,K) has been discovered. We have investigated the electronic properties of the undoped relative, solid picene, using a combination of experimental and theoretical methods. Our results provide detailed insight into the occuopied and unoccupied electronic states

Spatial correlations in hexagons generated via a Kerr nonlinearity

We consider the hexagonal pattern forming in the cross-section of an optical beam produced by a Kerr cavity, and we study the quantum correlations characterizing this structure. By using arguments related to the symmetry broken by the pattern formation, we identify a complete scenario of six-mode entanglement. Five independent phase quadratures combinations, connecting the hexagonal modes, are shown to exhibit sub-shot-noise fluctuations. By means of a non-linear quantum calculation technique, quantum correlations among the mode photon numbers are demonstrated and calculated.Comment: ReVTeX file, 20 pages, 7 eps figure

Detection of sub-shot-noise spatial correlation in high-gain parametric down-conversion

Using a 1GW-1ps pump laser pulse in high gain parametric down-conversion allows us to detect sub-shot-noise spatial quantum correlation with up to one hundred photoelectrons per mode, by means of a high efficiency CCD. The statistics is performed in single-shot over independent spatial replica of the system. The paper highlights the evidence of quantum correlation between symmetrical signal and idler spatial areas in the far field, in the high gain regime. In accordance with the predictions of numerical calculations the observed transition from the quantum to the classical regime is interpreted as a consequence of the narrowing of the down-converted beams in the very high gain regime.Comment: 4,2 pages, 4 figure

Polarization quantum properties in type-II Optical Parametric Oscillator below threshold

We study the far field spatial distribution of the quantum fluctuations in the transverse profile of the output light beam generated by a type II Optical Parametric Oscillator below threshold, including the effects of transverse walk-off. We study how quadrature field correlations depend on the polarization. We find spatial EPR entanglement in quadrature-polarization components: For the far field points not affected by walk-off there is almost complete noise suppression in the proper quadratures difference of any orthogonal polarization components. We show the entanglement of the state of symmetric intense, or macroscopic, spatial light modes. We also investigate nonclassical polarization properties in terms of the Stokes operators. We find perfect correlations in all Stokes parameters measured in opposite far field points in the direction orthogonal to the walk-off, while locally the field is unpolarized and we find no polarization squeezing.Comment: 16 pages, 18 figure

Physical properties of the sub-micrometer aerosol over the Amazon rain forest during the wet-to-dry season transition - comparison of modeled and measured CCN concentrations

Sub-micrometer atmospheric aerosol particles were studied in the Amazon region, 125 km northeast of Manaus, Brazil (-1°55.2'S, 59°28.1'W). The measurements were performed during the wet-to-dry transition period, 4-28 July 2001 as part of the LBA (Large-Scale Biosphere Atmosphere Experiment in Amazonia) CLAIRE-2001 (Cooperative LBA Airborne Regional Experiment) experiment. The number size distribution was measured with two parallel differential mobility analyzers, the hygroscopic growth at 90% RH with a Hygroscopic Tandem Mobility Analyzer (H-TDMA) and the concentrations of cloud condensation nuclei (CCN) with a cloud condensation nuclei counter. A model was developed that uses the H-TDMA data to predict the number of soluble molecules or ions in the individual particles and the corresponding minimum particle diameter for activation into a cloud droplet at a certain supersaturation. Integrating the number size distribution above this diameter, CCN concentrations were predicted with a time resolution of 10 min and compared to the measured concentrations. During the study period, three different air masses were identified and compared: clean background, air influenced by aged biomass burning, and moderately polluted air from recent local biomass burning. For the clean period 2001, similar number size distributions and hygroscopic behavior were observed as during the wet season at the same site in 1998, with mostly internally mixed particles of low diameter growth factor (~1.3 taken from dry to 90% RH). During the periods influenced by biomass burning the hygroscopic growth changed slightly, but the largest difference was seen in the number size distribution. The CCN model was found to be successful in predicting the measured CCN concentrations, typically within 25%. A sensitivity study showed relatively small dependence on the assumption of which model salt that was used to predict CCN concentrations from H-TDMA data. One strength of using H-TDMA data to predict CCN concentrations is that the model can also take into account soluble organic compounds, insofar as they go into solution at 90% RH. Another advantage is the higher time resolution compared to using size-resolved chemical composition data