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We use low-resolution optical lithography joined with solid state dewetting of crystalline, ultra-thin silicon on insulator (c-UT-SOI) to form monocrystalline, atomically smooth, silicon-based Mie resonators in well-controlled large periodic arrays. The dewetted islands have a typical size in the 100 nm range, about one order of magnitude smaller than the etching resolution. Exploiting a 2 µm thick SiO2 layer separating the islands and the underlying bulk silicon wafer, we combine the resonant modes of the antennas with the etalon effect. This approach sets the resonance spectral position and improves the structural colorization and the contrast between scattering maxima and minima of individual resonant antennas. Our results demonstrate that templated dewetting enables the formation of defect-free, faceted islands that are much smaller than the nominal etching resolution and that an appropriate engineering of the substrate improves their scattering properties. These results are relevant to applications in spectral filtering, structural color and beam steering with all-dielectric photonic devices.

Micro-satellites equipped with multispectral payloads are now under development to acquire information on the radiation reflected and emitted from the earth in the vis-NIR-TIR bands. In this framework, we are studying different approaches based on the compressive sampling technique supported by innovative multispectral detectors, where the image sampling is performed on the telescope focal plane with a Digital Micromirror Device (DMD). We will describe in the paper the possibilities and the constraints given by the use of the DMD in the focal plane. The optical design of the telescope, relay system and detector in two different application cases will be provided.

Rubidium and cesium metal nanoparticles were grown in nanoporous silica samples placed in alkali vapor cells. Their size and shape were investigated by measuring the sample optical transmittance. Spectral changes due to photodesorption processes activated by weak light were also analyzed. Alkali atoms photoejected from the silica walls diffuse through and out of the nanopores, modifying both the nanoparticle distribution in the silica matrix and the atomic vapor pressure in the cell volume. The number of rubidium and cesium atoms burst out of the samples was measured as a function of photon energy and fluence. The optical absorption measurements together with the analysis of the photodesorption yield give a complete picture of the processes triggered by light inside the nanopores. We show that atomic photodesorption, upon proper choice of light frequency and intensity, induces either growth or evaporation of nanosized alkali metal clusters. Cluster size and shape are determined by the host-guest interaction.

A new facility has been constructed at the INFN Legnaro National Laboratory (LNL) for the production of francium isotopes via a fusion-evaporation nuclear reaction and a laser laboratory has been set up for francium trapping. Francium is produced inside a gold target and after diffusion desorbs from its surface as an ion. A secondary beam line delivers the francium ions to the trapping cell where they are neutralized and trapped in a magneto-optical trap (MOT). Details on the production, delivery and neutralization methods are presented. Preliminary results on trapped francium are also shown. Production rate of ≃ 10 6 ions/s and a trap population of about 100 atoms have been achieved.

At present the most interesting technology for the preparation of advanced opto-electronic devices seems to be the one based on semiconductor nanowires (NWs). Because of their high aspect ratio the NWs are the best candidates for the combination of highly mismatched semiconductors while maintaining good crystal quality. In particular, thanks to strain relaxation at the NW sidewalls, a reduction of the misfit dislocation density is possible, which is highly beneficial for device applications. In this regard interface sharpness is also a critical issue, especially for InAs/GaAs. In this work we present a study of the structure and strain relaxation in InAs/GaAs axial nanostructures in self-assisted NWs grown by MBE on (111) Si substrates. The growth was performed without the use of any catalyst. The top InAs segment is grown on the bottom self-assisted GaAs part of the NW via a two-step process by supplying In and As separately. The samples have been studied by High Resolution TEM (HR-TEM) as well as Scanning TEM (STEM) with a HAADF (High Angle Annular Dark Field) detector. HR-TEM showed that the InAs/GaAs is sharp at the atomic level, a result that has never been reported in the literature for MBE grown InAs/GaAs NWs. By STEM-HAADF the chemical transition between GaAs and InAs was seen to occur abruptly over a distance of 1.5 nm across the interface. The strain relaxation and related misfit dislocation (MD) generation were investigated by mapping the strain distribution obtained by processing HR-TEM images of the interface by the Geometrical Phase Analysis (GPA) method. MDs were detected as expected due to the size of about 70 nm of the NWs. However, their mutual distance increases radially on going from the NW center towards the sidewalls confirming that the strain was partially relaxed elastically at the sidewalls thus decreasing the formation probability of the MDs, i.e. their density. The latter experimental results have been compared with FEM (Finite Element Method) calculations with excellent agreement.

Fast epitaxial growth on deeply patterned substrates is a very promising method to get epilayers of high structural quality, as layer cracking and wafer bowing can be avoided (C. V. Falub et al., Science 335, 1330 (2012). This approach is applied here to grow crack-free GaAs microcrystals on Si pillars which is a typical hetero system of interest in the field of the monolithic integration of III-V's on Si. The (001) offcut Si substrate was patterned into square pillars of various size by deep reactive ion etching (DRIE). 2 µm thick GaAs was then deposited by MBE at 580 °C at a rate of 0.5 ML/s with V/III=50. The defect analysis was carried out by TEM, HR-TEM, STEM-ADF (Annular Dark Field) and GPA (Geometrical Phase Analysis). The GaAs deposits were 2 µm high. The anti-phase domains were located only at the interface and their density was drastically limited by the substrate offcut. Threading dislocations (TDs) were present but were confined to the bottom 500 nm of the GaAs as they annihilated each another or bent back to the interface due to mutual interactions. They did not reach the GaAs microcrystal top that will serve as active region in devices. The TDs originated from misfit dislocations of both 60° and edge type. Twins were also present originating at the interface very likely at the offcut substrate steps. Some of them reached the topmost part of GaAs. As no dangling bond is associated with twins, they should not be electrically active in devices.

We fabricate site-controlled, ordered arrays of embedded Ga nanoparticles on Si, using a combination of substrate patterning and molecular-beam epitaxial growth. The fabrication process consists of two steps. Ga droplets are initially nucleated in an ordered array of inverted pyramidal pits, and then partially crystallized by exposure to an As flux, which promotes the formation of a GaAs shell that seals the Ga nanoparticle within two semiconductor layers. The nanoparticle formation process has been investigated through a combination of extensive chemical and structural characterization and theoretical kinetic Monte Carlo simulations. © 2014 IOP Publishing Ltd.

Metal nanoparticles (NPs) present unique optical properties, which are very different from those of bulk material. The localized surface plasmon resonance of these particles results in strong optical scattering and a strongly enhanced optical near-field around the particle [1]. Recently, metal nanoparticles have been investigated as a possible way to improve the performance of thin-film solar cells [2]. Metal NPs embedded in a semiconductor material act as antennas for the incident light and store energy in the localized surface plasmon resonance. The strong near-field absorption enhancement can be used to reduce the thickness of a thin film solar cell without a reduction of optical absorption. Here we show that, by the combination of substrate patterning and droplet epitaxy [3], it is possible to obtain the fabrication of and ordered and controlled array of embedded Ga nanoparticles in a semiconductor matrix. A Si(001) wafer patterned with regular arrays of half micron inverted pyramid pits was used as substrate for the subsequent fabrication of GaAs islands in the droplet epitaxy (DE) growth mode. DE separates Ga deposition, used for the formation of an ensemble of localized Ga reservoirs on the surface, from the As supply, necessary to crystallize the droplets into GaAs nanostructures. Figure 1(a) shows a SEM image taken before pre-growth cleaning on a typical array of {111} pits, etched into a Si(001) substrate surface. Figure 1(b) is taken on the same sample after DE growth, showing that a dot is present at the base of each pit. The capture of the Ga droplet by the inverted pits is caused by capillarity forces. The occupancy ratio of the pits by Ga droplets, obtained from several similar images, is 80%. The chemical and structural quality of the GaAs nanoislands at the bottom of pits was studied by means of set of complementary characterization techniques. In particular cross-sectional TEM was employed in order to extract the exact shapes and composition of the islands. Figure 2 (a) shows such a cross sectional TEM image along a [110] direction through a tip of a pit after the Ga droplet crystallization process. The original shape of the pit is visible as a {111} inverted pyramid. Figures 2 (b) and (c) report the EDS maps of the characteristic x-ray K? emissions of Ga and As, respectively. Strongly different concentration profiles of Ga and As are easily observable. Ga fills uniformly the whole space occupied by the GaAs island from the tip of the pit upto the island surface. Arsenic is detected only in limited crust close at the island surface. Extracting the EDS spectrum from narrower areas along the vertical axis of the pit shows that the As:Ga ratio nearly approaches 1 at the very top of the As map whereas it strongly decreases on going deeper in the island. The inner part of the island is constituted by a pure Ga NP. This NP is then fully embedded within a semiconductor matrix, constituted by the pit Si sidewalls and the GaAs crust which is formed during the crystallization process with As. Monte Carlo simulations (MC) examining nanostructural evolution in the Ga droplet nucleated in the pit during the crystallization process support the observed phenomenology. [1] C. F. Bohren and D. R. Huffman, Absorption and Scattering of Light by Small Particles (Wiley, 2008). [2] H. R. Stuart and D. G. Hall, Appl. Phys. Lett. 69, 2327 (1996). [3] N. Koguchi and K. Ishige, Japanese Journal of Applied Physics 32, 20522058 (1993). __________________________

One of the fundamental ingredients for quantum cryptography and quantum information applications is the fabrication of single and entangled photon emitters. Single photon emitter should produce exactly a single photon on demand, should work not only at cryogenic temperature and should be easy to produce and to integrate on existing electronic devices. In this work, we present the fabrication and characterization of single photon emission from high quality GaAs quantum dots (QDs) by droplet epitaxy (DE) and from impurity centers in AlGaAs layers grown on Si through a thin Ge buffer layer deposited by Low Energy Plasma Enhanced Chemical Vapour Deposition (LEPECVD). The deposition of a thin Ge layer by LEPECVD and subsequent annealing cycles allow for the reduction of threading dislocation density down to few 107 cm-2. DE is an intrinsically low thermal budget technique, being performed at temperatures between 200 and 350 °C. This makes DE perfectly suited for the implementation of growth procedures compliant with back-end integration of III-V nanostructures on CMOS. GaAs QDs with a density of few 108 cm-2 and a mean height of 8 nm are fabricated by DE inside a Al0.3Ga0.7As barrier. Bright and sharp emission lines are observed in a micro-photoluminescence experiment around 700 nm, with pure radiative excitonic lifetime and clear evidence of exciton-biexciton cascade. The achievement of quantum photon statistics is directly proved by antibunching in the second order correlation function as measured with a Hanbury Brown and Twiss interferometer up to T=80 K, thus making the single photon emitter working at liquid nitrogen temperature and compatible with present CMOS technology. The optical quality of the GaAs quantum dots grown on Si substrate is almost comparable with quantum dots directly grown on GaAs substrates. We also show that the epitaxial growth of thin layers of Al0.3Ga0.7As on GaAs buffer layers grown on Si and Ge substrates allows to obtain a single photon source by exploiting the strewn and unintentional contamination with defects of the Al0.3Ga0.7As. Very bright and sharp single photoluminescence lines are observed in confocal microscopy. These lines behave very much as single excitons in QDs, but their realization is by far much easier, since it does not require 3D nucleation or spatially selective doping. The photon antibunching is demonstrated by time resolved Hanbury Brown and Twiss measurements. In both cases (GaAs QDs by DE and impuritues in AlGaAs layer) it is clearly demonstrated a new procedure for the integration of high efficient light emitters, based on III-V semiconductors, directly on Si substrates, and opening the route to wide applications to optoelectronics, photonics and quantum information technology.

The integration of III-V nanostructures on silicon would open thè possibility to pursue integration between high performance quantum photonic devices and quantum informatimi technology devices based on CMOS circuitry on Si. In this work, we present thè growth and optical characterization of high quality GaAs quantum dots (as single photon emitters) grown by droplet epitaxy on Si substrates through thè deposition of a thin Gè layer. Droplet epitaxy [1] is intrinsically a lovv thermal budget growth, being performed at temperatures between 200 and 350 °C. This makes droplet epitaxy perfectly suited for thè realization of growth procedures compatible with back-end integration ofUI-V nanostructures on CMOS [2]. The contro! of thè growth kinetics allows thè fabrication of quantum dot samples with an arcai density down to few 10scm~~. Brighi and sharp emission lines are observed in a micro-photoluminescence experiment around 700 nm. with pure radiative excitonic lifetime and clear evidence of exciton-biexciton cascade. The achievement of quantum photon statistics is directly provedby antibunching in thè second order correlation function as measured with a Hanbury Brown and Twiss interferometer up to T=80 K, thus making thè single photon emitter working at liquid nitrogen temperature and compatible with present CMOS technology. Optical quality of thè GaAs quantum dots grown on Si substrate is almost comparable with quantum dots directly grown on GaAs substrates, clearly dernonstrating a new procedure for thè integration of high efficient light emitters, based on III-V semiconductors, directly on Si substrates, and opening thè route to wide applications to optoelectronics, photonics and quantum information technology. [1] N. Koguchi, S. Takahashi, T. Chikyow, J. Crystaì Growth 111 (1991) 688. [2] S. Bielli. C. Somaschini, S. Sanguinetti, N. Koguchi, G. Isella, and D. Chraslina, AppliedPhysics Lerters 95, 241102 (2009)

The titanium-doped sapphire (Ti:Al 2 O 3 ) laser has been established as the workhorse tunable solid-state laser for the near-infrared spectral range, for continuous-wave (cw) as well as ultrafast timescales, benefiting numerous applications. Ti:sapphire laser have relied mainly on argon ion lasers and frequency-doubled Nd-based green lasers as the pump source [1]. Other possible pumps include optically-pumped-semiconductor-lasers in the green, employing intracavity frequency-doubling and, more recently, GaN diode lasers in the blue, but with limitations of low output power and poor beam quality. Fiber lasers have recently attracted much attention for their compact design, robustness, power scalability with turnkey operation and cost effectiveness. The combination of a cw infrared fiber laser and a simple single-pass second-harmonic-generation scheme based on MgO:sPPLT is a potentially attractive route for high-power cw green generation [2]. Hence, it is worthwhile to explore its potential as a new pump architecture for the Ti:sapphire laser, which would provide a simple, high-power, compact, and cost-effective alternative to the traditional, cw solid-state green sources.

A transferable version of the bond charge model (BCM), suitable to treat sp(2) configurations like fullerenes and graphite, has been extended to the calculation of Raman and infrared spectral intensities. The cluster polarizability has been derived consistently with the model. No additional parameter, besides the model parameters entering the dynamical matrix is required. Through its simple modelling of electron-phonon interaction, the model shows an excellent agreement with the experimental spectral intensities of C-60. The method allows for an unambiguous assignment of the theoretical frequencies to the experimental peaks in more complex systems such as C-70.

A density-functional approach based on Wannier-function type orbitals is presented for calculating extended defect formation energies in semiconductors. The energy contributions are ascribed to the localized orbitals where defect formation energy contributions turn out to rapidly decrease with increasing distance from the defect. Results for ideal lattice properties and the energy of the twin grain boundary, stacking faults, and Σ = 9 〈110〉-tilt grain boundary agree well with literature values. Ein Dichte-Funktional-Schema mit lokalisierten Orbitalen ahnlich den Wannier-Funktionen zur Berechnung der Energien ausgedehnter Defekte wird vorgestellt. Die Energiebeitrage werden darin den lokalisierten Orbitalen zugeordnet, wobei die Beitrage zu den Defekt-Bildungsenegien mit zunehmendem Abstand vom Defekt rasch abnehmen. Die Ergebnisse fur Eigenschaften des idealen Gitters und fur die Energie von Zwillings-Korngrenzen, Stapelfehlern und der Σ = 9 〈110〉-Kipp-Korngrenze in Silizium stimmen gut mit Literaturwerten uberein.

We report resistivity measurements in the temperature range 0.15-1.2 K Performed on non-compensated Si:As samples doped by ion implantation on the insulating side of the metal-insulator transition. The data show a crossover of the variable-range-hopping (VRH) resistivity dependence rho(T) from rho is-proportional-to exp(T1/4/T)1/4 (Mott VRH predicted behaviour) to rho is-proportional-to exp(T1/2/T)1/2, which demonstrates the persistence of a Coulomb pp in the density of states even in the vicinity of the critical concentration. The simultaneous observation of the T1/4 and T1/2 parameters allows the determination of the effective size of the pp.

A model accounting for the time dependence of shape fluctuations in metal microclusters and their effect on the damping width of the plasmon resonance is discussed. An estimate of the relaxation time of the quadrupole shape is given, and calculations demonstrating the effects of time-dependent thermal fluctuations on the plasmon in K9+ are presented.

An interferometric method is used to improve the accuracy of the 7S-7P transition frequencies of three francium isotopes by 1 order of magnitude. The deduced isotope shifts for 209-211Fr confirm the ISOLDE data. The frequency of the D2 transition of 212Fr--the accepted reference for all Fr isotope shifts--is revised, and a significant difference with the ISOLDE value is found. Our results will be a benchmark for the accuracy of the theory of Fr energy levels, a necessary step to investigate fundamental symmetries.

We report the first measurement of the diffusion coefficients of francium and rubidium ions implanted in a yttrium foil. We developed a methodology, based on laser spectroscopy, which can be applied to radioactive and stable species, and allows us to directly take record of the diffusion time. Francium isotopes are produced via fusion-evaporation nuclear reaction of a 100 MeV 18-O beam on a Au target at the Tandem XTU accelerator facility in Legnaro, Italy. Francium is ionized at the gold-vacuum interface and Fr+ ions are then transported with a 3 keV electrostatic beamline to a cell for neutralization and capture in a magneto-optical trap (MOT). A Rb+ beam is also available, which follows the same path as Fr+ ions. The accelerated ions are focused and implanted in a 25 um thick yttrium foil for neutralization: after diffusion to the surface, they are released as neutrals, since the Y work function is lower than the alkali ionization energies. The time evolution of the MOT and the vapor fluorescence signals are used to determine diffusion times of Fr and Rb in Y as a function of temperature., Comment: 7 pages, 8 figures

The apparatus for the production and trapping of francium is described and its performances are reported. Latest results on magneto-optical trapping of Francium are summarized: trapping of 209, 210, 211 Francium isotopes, measurements of their trapping frequencies, measurements of diffusion parameters of Francium ions in yttrium. Future experiments on fundamental physics are presented.

Francium is one of the best candidates for atomic parity nonconservation (APNC) and for the search of permanent electric dipole moments (EDMs). APNC measurements test the weak force between electrons and nucleons at very low momentum transfers. They also represent a unique way to detect weak nucleon-nucleon interactions. EDMs are instead related to the time-reversal symmetry. Preliminary to these fundamental measurements are precision studies in atomic spectroscopy and the development of magneto-optical traps (MOT), which partially compensate for the lack of stable Fr isotopes. At LNL Legnaro, francium is produced by fusion of 100-MeV 18O with 197Au in a thick target, followed by evaporation of neutrons from the compound nucleus. Francium diffuses inside the hot target (1200 K) and is surface ionized for injection at 3 keV in an electrostatic beamline. Typically, we produce 1×106 (210Fr ions)/s for a primary flux of 1.5×1012 particles/s. We have studied Fr yields as a function of primary beam energy, intensity, and target temperature. Information on the efficiency of bulk diffusion, surface desorption and ionization is deduced. The beam then enters a Dryfilm-coated cell, where it is neutralized on a heated yttrium plate. The escape time of neutral Fr (diffusion + desorption) is approximately 20 s at 950 K, as measured with a dedicated setup. In the MOT, we use 6 orthogonal Ti:sapphire laser beams for the main pumping transition and 6 beams from a stabilized diode repumper. Fluorescence from trapped atoms is observed with a cooled CCD camera, in order to reach noise levels from stray light equivalent to approximately 50 atoms. Systematic tests are being done to improve the trapping efficiency. We plan to further develop Fr traps at LNL; in parallel, we will study APNC and EDM techniques and systematics with stable alkalis at Pisa, Siena, and Ferrara.

We present the Trap-rad experiment, which in the long term aims to an atomic parity violation (APV) measurement in francium isotopes. We describe the present status of the experiment, the francium production and the magneto-optical trap (MOT). Some details are given about our new CCD detection system. We explore then the possibility to perform APV measurements with francium. The low Trap-rad francium production rates should allow to perform preliminary tests. With higher rates attainable in other accelerator facilities, it should be possible to begin a francium APV experiment.

We present the detection of a two-photon transition based on stimulated emission. This measurement was performed in rubidium for the 5S-5D{sub 5{approx}}{sub sol{approx}}{sub 2}-5P{sub 3{approx}}{sub sol{approx}}{sub 2} transition, using two low-cost diode lasers. Several detection schemes were tested. We reached the best results by probing the circular birefringence of the excited vapor, with the polarization analysis of the amplified laser beam.

We describe the production of francium beams from the fusion–evaporation reaction Au 197 ( O 18 , kn ) 215 - k Fr generated by a ∼ 100 MeV O 6 + 18 beam on a thick gold target. The physics of the production process is discussed, together with estimates of expected production rates. The production target is heated to ∼ 1200 K and kept at a potential of + 3 kV to enhance Fr diffusion and surface desorption, and to accelerate surface-ionized ions. Details are given on its design and construction. The performance of the target is measured as a function of primary beam energy and flux, target temperature and extraction voltage. Average production rates are 0.7 × 10 6 ions / s for 210Fr with a primary beam flux of 10 12 particles / s , with peaks of 2 × 10 6 ions / s . From these measurements, information on the efficiency of the release processes is inferred.

Waste stabilization ponds (WSP) are an often-used option to treat faecal sludges collected from on-site sanitation systems. Since agricultural use is one of the most attractive options for sludge disposal, specific guidelines on the hygienic sludge quality must be fulfilled, such as for viable helminth eggs and Salmonella sp. Although Salmonella isolation methods are well known for other types of samples, they are not suitable for faecal sludge. The reason can be attributed to the co-existence of a native bacterial sludge flora masking Salmonella development, especially if this bacteria is present at low concentrations. In order to select the best methodology for Salmonella recovery from septage sludge, different culture media were assayed at different incubation periods and temperatures. The proposed methodology for Salmonella recovery from sludge can be summarised as follows: (1) enrichment in Rappaport-Vassiliadis broth at 43 degrees C, 48 hours, and (2) isolation in XLD agar at 40 degrees C, 24 hours. Identification of suspected colonies by biochemical tests: TSI, LIA, urease and serological confirmation with Group O Antigen.

Sludge management arises as a relevant problem after being accumulated in primary ponds of septage treatment plants. One of the most attractive options for sludge disposal is its use in agriculture and then specific guidelines regarding hygienic quality must be fulfilled. This study aimed at evaluating the storage time needed to inactivate Ascaris eggs and Salmonella in sludge accumulated in a primary pond treating septage. Raw septage exhibited very low concentrations of viable Ascaris eggs, thus experiments with Ascaris suum eggs spiking were conducted. The concentration of Ascaris eggs in the solids accumulated at the bottom of the pond was 20 eggs/g of total solids (g TS) at the time of pond closure. Although it decreased, some eggs remained viable (0.59 mean viable eggs/g TS) up to 20 months of in-pond storage of the biosolids. Salmonella survival was studied after developing an analytical method that inhibited the native flora. Sludge was seeded with Salmonella enteritidis. An equation adequately describing Salmonella die-off in biosolids subjected to 115 days of in-pond storage/dewatering, was found to be represented by the regression: y = log MPN Salmonella/g TS = 6.67 x t(-0.086), with t = storage time elapsed in days. The initial concentration was 7.0 x 10(6) MPN/g TS and the removal efficiency was 99%.

Five municipal sewers with small flow rates (Manarola, Riomaggiore, Portovenere, Tellaro, Bocca di Magra) were studied using the Microtox® test and a bacterial luminescence bioassay in order to evaluate the water quality in these areas of the eastern Ligurian coast. The work was performed including chemical analysis, microbiological and ecotoxicological assays. Analyses were carried out on both the effluents and the water body close to the pipe discharge. None of the measured chemical parameters exceeded the permitted limits, both in the effluents and in the seawater samples, even if some slightly critical situations were highlighted by the Microtox® test on the effluents. On the other hand, the Microtox® appeared to be less effective than another ecotoxicological assay based on the luminescent fraction of epibacteria for the evaluation of seawater quality. The good water quality of the considered areas was assessed although a slightly worse condition was encountered in Bocca di Magra.

We have detected, by using stimulated emission, an atomic parity violation (APV) in the form of a chiral optical gain of a cesium vapor on the $7S\mathrm{\text{\ensuremath{-}}}6{P}_{3/2}$ transition, consecutive to linearly polarized $6S\mathrm{\text{\ensuremath{-}}}7S$ excitation. We demonstrate the validity of this detection method of APV, by presenting a 9% accurate measurement of expected sign and magnitude. We stress several advantages of this new approach which fully exploits the cylindrical symmetry of the setup. Future measurements at the percent level will provide an important cross-check of an existing more precise result obtained by a different method.

We have detected, by using stimulated emission, an atomic parity violation (APV) in the form of a chiral optical gain of a cesium vapor on the 7S-6P(3/2) transition, consecutive to linearly polarized 6S-7S excitation. We demonstrate the validity of this detection method of APV, by presenting a 9% accurate measurement of expected sign and magnitude. We stress several advantages of this new approach which fully exploits the cylindrical symmetry of the setup. Future measurements at the percent level will provide an important cross-check of an existing more precise result obtained by a different method.

We observe charge multiplication of photoemitted electrons in cylindrical alumina cells, containing cesium vapor, submitted to a longitudinal electric field and to intense laser pulses. We present several diagnoses allowing us to attribute this charge multiplication to efficient secondary electron emission (SEE) from the accelerated photoelectrons colliding with the inner wall at grazing incidence. Machining millimeter-size triangular grooves on the initially smooth inner wall, so as to prevent grazing incidence, is shown to be efficient in reducing SEE. The atomic signal characteristic of the space charge accumulated close to the anode is found to be reduced by more than one order of magnitude. This result is of important significance, not only for our parity-violation experiment in cesium vapor, but also for experiments and techniques involving SEE at grazing incidence.

A Nd:YVO4 laser, end-pumped by a fiber-coupled diode laser, provides 40% slope efficiency, a nearly diffraction-limited beam and 6.5 W of output power at 1.34 |im, the highest so far reported for this host. The use of crystals with a very low Nd concentration is a key element for performance improvement.

A full-scale (30 cubic meters) test chamber was developed for the study of the effects of volatile organic compounds (VOC) emissions from materials in real indoor environments. This test chamber is located outdoor and was designed to optimize the realism of the test. The chamber is supplied with unfiltered air and is realized in concrete with gypsum-finished walls and ceiling. The air supply system allows the operation in static conditions (no air change) and dynamic conditions (controlled air change). An arbitrary time schedule of different air change rates can be established in order to simulate variable indoor conditions. A ceiling fan assures the proper air mixing. The temperature control system is based on electrical heating elements in winter, while in summer the temperature is given by a balance of the solar radiation, the thermal inertia of the chamber structure, the temperature of external air and the air change rate.

A Nd:YVO4 laser, end-pumped by a fiber-coupled diode-laser array, generates 7.3 W of output power at 1342 nm, the highest so far reported for this host crystal. The slope efficiency is 40% and the output-beam divergence is close to the diffraction limit. An important point in attaining such results is the choice of crystals with low Nd concentration.

We have investigated the production of the BSCCO 2223 phase by using four different types of starting chemical compounds with the same thermal treatment. Samples have been characterised in various aspects, and the 2223 phase volume fractions have been accurately determined by applying the effective medium theory to magnetic susceptibility measurements. The results show that polycrystalline samples are well described by the spherical inclusion granular model, and that organic precursors strongly inhibit the production of the 2223 phase with respect to inorganic ones.

A very simple but effective accessory, based on a couple of large area silicon photodiodes, is presented. It allows the analysis, by a conventional double-beam ultraviolet-visible spectrophotometer, of scattering samples. The accessory, very low in cost, can be installed and removed quickly and can be easily constructed by the users to match different commercial models. The layout and the wiring diagram of the unit are described and the performances are tested. (C) 1997 American Institute of Physics. [S0034-6748(97)01311-7].

We present a study of the thermodynamical properties of C60 in the microcanonical ensemble. Solidlike and metastable liquidlike form can be identified in the low energy and in the high energy range, respectively. The transition between the two phases is characterized by a finite energy range, in agreement with general theories of cluster melting. In particular, we have observed that the melting is preceded by a highly isomerized transition region where a sizeable atomic mobility is achieved via hopping between different isomer structures. © 1995 American Institute of Physics.

We present low-temperature resistivity measurements, carried out in the temperature range 100400 mK on uncompensated Si:P samples doped by ion implantation in the just-metallic side of the metal-insulator transition. As the dopant concentration increases the experimental data confirm the presence of the change of sign in the T -dependent correction to the conductivity, with a cusplike behavior of the critical prefactor. However, the sign transition is followed by the turning on of an anomalous temperature contribution. We analyze both features in terms of renormalization of electron-electron interaction effects and show that in Si:P the effective-electron-coupling constant has a sizable enhancement both with doping and temperature. © 1995 The American Physical Society.

The effects of hypoxia on prostanoid production were studied in atria from normal, acute diabetic and insulin-treated diabetic rats. Diabetes was induced by intravenous administration of 65 mg/kg of streptozotocin, the rats were killed 5 days later. Hypoxia was performed by incubation of the atria during 60 min in nitrogen-equilibrated glucose free Krebs' solution followed by 15 min of reoxygenation. The prostanoids 6-keto prostaglandin F1 alpha (6-keto PGF1 alpha) and thromboxane B2 (TXB2), stable metabolites of prostacyclin and TXA2, respectively, as well as PGF2, were measured by reversed phase HPLC-UV. In control atria, the production of 6-keto PGF1 alpha was equivalent to that of PGE2, whereas TXB2 was released in a much smaller amount. In diabetic atria, 6-keto PGF1 alpha production was reduced by 65%, whereas TXB2 release was increased by 158% compared to the controls. When the normal atria were exposed to 60 min of hypoxia, the release of 6-keto PGF1 alpha increased by 142% compared to basal values and remained elevated after 15 min of reoxygenation whereas in diabetic and insulin-treated diabetic tissues the 6-keto PGF1 alpha production was not modified by the hypoxia-reoxygenation period. The release of TXB2 was increased after 60 min hypoxia in normal as well as in diabetic and insulin-treated diabetic tissues and remained elevated during the reoxygenation. The PGE2 output increased only after the onset of the reoxygenation in the three groups studied.(ABSTRACT TRUNCATED AT 250 WORDS)

Reflectance (R) and trasmittance (T) of C60 single-crystals have been measured in the 400-5000 cm-1 range, at room temperature, by using micro-Fourier transform IR spectroscopy. The frequencies of the peaks, appearing in both R and T spectra, are compared with the IR active ones calculated for the simple cubic structure with the bond charge model. It appears that all modes which are expected from symmetry arguments to give a dipole activity are actually observed and the corresponding frequencies are in good agreement with the experimental findings.

The vibrational analysis ofsp 2-bonded carbon clusters with different nearest-neighbour interatomic distances (2 in C60, 8 in C70), performed in the framework of the bond-charge model, leads to the determination of an exponential form for the short-range interatomic potential which is inclusive of charge transfer effects. The potential, besides leading to excellent agreement with the existing spectroscopic data andab initio Car-Parrinello calculations, ensures a good transferability of the model to other clusters and possibly an empirical basis for molecular dynamics simulations.

A facility for the production of radioactive francium is operating at the laboratories of the Istituto Nazionale di Fisica Nucleare (INFN) in Legnaro, Italy. The goal is to collect a cold sample of radioactive atoms in a magneto-optical trap for studies in atomic, nuclear, and particle physics. Production of francium is achieved via the fusion-evaporation reaction Au197(O18,kn)215−kFr generated by a ∼100‐MeV O6+18 beam on a thick gold target. The production target is heated to ∼1200K and kept at a potential of +3kV to enhance Fr diffusion and surface desorption. Average production rates are 0.7×106ions∕s for Fr210 with a primary beam flux of 1012particles∕s, with peaks of 2×106ions∕s. Details are given on the design and construction of the production targets and on the measurements that characterize their performance.

Laser cooling and trapping offers the possibility of confining a sample of radioactive atoms in free space. Here, we address the question of how best to take advantage of cold atom properties to perform the observation of as highly forbidden a line as the 6S-7S Cs transition for achieving, in the longer term, Atomic Parity Violation measurements in radioactive alkali isotopes. Another point at issue is whether one might do better with stable, cold atoms than with thermal atoms. To compensate for the large drawback of the small number of atoms available in a trap, one must take advantage of their low velocity. To lengthen the time of interaction with the excitation laser, we suggest choosing a geometry where the laser beam exciting the transition is colinear to a slow, cold atomic beam, either extracted from a trap or prepared by Zeeman slowing. We also suggest a new observable physical quantity manifesting APV, which presents several advantages:specificity, efficiency of detection, possibility of direct calibration by a parity conserving quantity of a similar nature. It is well adapted to a configuration where the cold atomic beam passes through two regions of transverse, crossed electric fields, leading both to differential measurements and to strong reduction of the contributions from the M_1-Stark interference signals, potential sources of systematics in APV measurements. Our evaluation of signal to noise ratios shows that with available techniques, measurements of transition amplitudes, important as required tests of Atomic Theory should be possible in cesium 133 with a statistical precision of 1/1000 and probably also in Fr isotopes for production rates of 10^6 Fr atoms/s., Comment: 13 pages, 4 figures, 1 table