847 research outputs found
Synthesis and characterization of attosecond light vortices in the extreme ultraviolet
Infrared and visible light beams carrying orbital angular momentum (OAM) are
currently thoroughly studied for their extremely broad applicative prospects,
among which are quantum information, micromachining and diagnostic tools. Here
we extend these prospects, presenting a comprehensive study for the synthesis
and full characterization of optical vortices carrying OAM in the extreme
ultraviolet (XUV) domain. We confirm the upconversion rules of a femtosecond
infrared helically phased beam into its high-order harmonics, showing that each
harmonic order carries the total number of OAM units absorbed in the process up
to very high orders (57). This allows us to synthesize and characterize
helically shaped XUV trains of attosecond pulses. To demonstrate a typical use
of these new XUV light beams, we show our ability to generate and control,
through photoionization, attosecond electron beams carrying OAM. These
breakthroughs pave the route for the study of a series of fundamental phenomena
and the development of new ultrafast diagnosis tools using either photonic or
electronic vortices
First Results of the Phase II SIMPLE Dark Matter Search
We report results of a 14.1 kgd measurement with 15 superheated droplet
detectors of total active mass 0.208 kg, comprising the first stage of a 30 kgd
Phase II experiment. In combination with the results of the neutron-spin
sensitive XENON10 experiment, these results yield a limit of |a_p| < 0.32 for
M_W = 50 GeV/c2 on the spin-dependent sector of weakly interacting massive
particle-nucleus interactions with a 50% reduction in the previously allowed
region of the phase space formerly defined by XENON, KIMS and PICASSO. In the
spin-independent sector, a limit of 2.3x10-5 pb at M_W = 45 GeV/c2 is obtained.Comment: 4 pages, 4 figures; PRL-accepted version with corrected SI contour
(Fig. 4
Final Analysis and Results of the Phase II SIMPLE Dark Matter Search
We report the final results of the Phase II SIMPLE measurements, comprising
two run stages of 15 superheated droplet detectors each, the second stage
including an improved neutron shielding. The analyses includes a refined signal
analysis, and revised nucleation efficiency based on reanalysis of
previously-reported monochromatic neutron irradiations. The combined results
yield a contour minimum of \sigma_{p} = 4.2 x 10^-3 pb at 35 GeV/c^2 on the
spin-dependent sector of WIMP-proton interactions, the most restrictive to date
from a direct search experiment and overlapping for the first time results
previously obtained only indirectly. In the spin-independent sector, a minimum
of 3.6 x 10^-6 pb at 35 GeV/c^2 is achieved, with the exclusion contour
challenging the recent CoGeNT region of current interest.Comment: revised, PRL-accepted version with slightly weakened limit contour
The SIMPLE Phase II Dark Matter Search
Phase II of SIMPLE (Superheated Instrument for Massive ParticLe Experiments)
searched for astroparticle dark matter using superheated liquid
CClF droplet detectors. Each droplet generally requires an energy
deposition with linear energy transfer (LET) 150 keV/m for a
liquid-to-gas phase transition, providing an intrinsic rejection against
minimum ionizing particles of order 10, and reducing the backgrounds to
primarily and neutron-induced recoil events. The droplet phase
transition generates a millimetric-sized gas bubble which is recorded by
acoustic means. We describe the SIMPLE detectors, their acoustic
instrumentation, and the characterizations, signal analysis and data selection
which yield a particle-induced, "true nucleation" event detection efficiency of
better than 97% at a 95% C.L. The recoil- event discrimination,
determined using detectors first irradiated with neutrons and then doped with
alpha emitters, provides a recoil identification of better than 99%; it differs
from those of COUPP and PICASSO primarily as a result of their different
liquids with lower critical LETs. The science measurements, comprising two
shielded arrays of fifteen detectors each and a total exposure of 27.77 kgd,
are detailed. Removal of the 1.94 kgd Stage 1 installation period data, which
had previously been mistakenly included in the data, reduces the science
exposure from 20.18 to 18.24 kgd and provides new contour minima of
= 4.3 10 pb at 35 GeV/c in the
spin-dependent sector of WIMP-proton interactions and = 3.6
10 pb at 35 GeV/c in the spin-independent sector. These
results are examined with respect to the fluorine spin and halo parameters used
in the previous data analysis.Comment: 20 pages, 19 figures; accepted Physical Review
The effect of cocaine on gastric mucosal PGE2, LTC4 and ulcerations
The association between cocaine use and acute gastroduodenal perforation is known. The effect of cocaine and stress on gastric mucosal ulceration and the levels of prostaglandin E2 (PGE2) and leukotriene C4 (LTC4) was studied in 40 Sprague–Dawley rats. Controls received intraperitoneal (i.p.) saline, ten received i.p. cocaine (35 mg/kg), ten were stressed by the cold restraint method, and ten had i.p. cocaine and stress. Cocaine alone did not induce ulceration, but decreased PGE2 levels. Stress alone caused ulceration, but was not associated with a change in either PGE2 or LTC4 levels. When combined with stress, however, cocaine caused a three-fold increase in ulceration and a significant increase in PGE2 and LTC4 levels. Stress may predispose the cocaine addict to loss of gastroduodenal mucosal integrity, which is related to an imbalance of PGE2 and LTC4 synthesis
PHIL photoinjector test line
LAL is now equiped with its own platform for photoinjectors tests and
Research and Developement, named PHIL (PHotoInjectors at LAL). This facility
has two main purposes: push the limits of the photoinjectors performances
working on both the design and the associated technology and provide a low
energy (MeV) short pulses (ps) electron beam for the interested users. Another
very important goal of this machine will be to provide an opportunity to form
accelerator physics students, working in a high technology environment. To
achieve this goal a test line was realised equipped with an RF source, magnets
and beam diagnostics. In this article we will desrcibe the PHIL beamline and
its characteristics together with the description of the first two
photoinjector realised in LAL and tested: the ALPHAX and the PHIN RF Guns
Complementary Patents and Market Structure
Many high technology goods are based on standards that require several essential patents owned by different IP holders. This gives rise to a complements and a double mark-up problem. We compare the welfare effects of two different business strategies dealing with these problems. Vertical integration of an IP holder and a downstream producer solves the double mark-up problem between these firms. Nevertheless, it may raise royalty rates and reduce output as compared to non-integration. Horizontal integration of IP holders solves the complements problem but not the double mark-up problem. Vertical integration discourages entry and reduces innovation incentives, while horizontal integration always benefits from entry and innovatio
Spectrally resolved multi-channel contributions to the harmonic emission in N 2
International audienceWhen generated in molecules, high-order harmonics can be emitted through different ionization channels. The coherent and ultrafast electron dynamics occurring in the ion during the generation process is directly imprinted in the harmonic signal, i.e. in its amplitude and spectral phase. In aligned N2 molecules, we find evidence for a fast variation of this phase as a function of the harmonic order when varying the driving laser intensity. Basing our analysis on a three-step model, we find that this phase variation is a signature of transitions from a single- to a multi-channel regime. In particular, we show that significant nuclear dynamics may occur in the ionization channels on the attosecond timescale, affecting both the amplitude and the phase of the harmonic signal
Molecular orbital tomography from multi-channel harmonic emission in N2
International audienceHigh-order harmonic generation in aligned molecules can be used as an ultrafast probe of molecular structure and dynamics. By characterizing the emitted signal , one can retrieve information about electronic and nuclear dynamics occurring in the molecule at the attosecond timescale. In this paper , we discuss the theoretical and experimental aspects of molecular orbital tomography in N 2 and investigate the influence of multi-channel ionization on the orbital imaging. By analyzing the spectral phase of the harmonic emission as a function of the driving laser intensity , we address two distinct cases , which in principle allow the orbital reconstruction. First , the contributions from two molecular orbitals could be disentangled in the real and imaginary parts of the measured dipole , making it possible to reconstruct both orbitals. Second , by decreasing the driving laser intensity , the transition from a multi-channel to a single-channel ionization regime is shown. The highest occupied molecular orbital may then be selected as the only one contributing efficiently to the harmonic emission. The latter approach paves the way towards the generalization of tomography to more complex systems
Kerr self-cleaning of pulsed beam in an ytterbium doped multimode fiber
We experimentally demonstrate that Kerr spatial self-cleaning of a pulsed beam
can be obtained in an amplifying multimode optical fiber. An input peak power of 500 W
only was sufficient to produce a quasi-single-mode emission from the double-clad ytterbium
doped multimode fiber (YMMF) with non-parabolic refractive index profile. We compare the
self-cleaning behavior observed in the same fiber with loss and with gain. Laser gain
introduces new opportunities to achieve spatial self-cleaning of light in multimode fibers at a
relatively low power threshold
- …