2,788 research outputs found
Pulsed source of energetic atomic oxygen
A pulsed high flux source of nearly monoenergetic atomic oxygen was designed, built, and successfully demonstrated. Molecular oxygen at several atmospheres pressure is introduced into an evacuated supersonic expansion nozzle through a pulsed molecular beam valve. An 18 J pulsed CO2 TEA laser is focused to intensities greater than 10(9) W/sq cm in the nozzle throat to generate a laser-induced breakdown. The resulting plasma is heated in excess of 20,000 K by a laser supported detonation wave, and then rapidly expands and cools. Nozzle geometry confines the expansion to provide rapid electron-ion recombination into atomic oxygen. Average O atom beam velocities from 5 to 13 km/s were measured at estimated fluxes to 10(18) atoms per pulse. Preliminary materials testing has produced the same surface oxygen enrichment in polyethylene samples as obtained on the STS-8 mission. Scanning electron microscope examinations of irradiated polymer surfaces reveal an erosion morphology similar to that obtained in low Earth orbit, with an estimated mass removal rate of approx. 10(-24) cu cm/atom. The characteristics of the O atom source and the results of some preliminary materials testing studies are reviewed
A pulsed source of continuous variable polarization entanglement
We have experimentally demonstrated polarization entanglement using
continuous variables in an ultra-short pulsed laser system at telecommunication
wavelengths. Exploiting the Kerr-nonlinearity of a glass fibre we generated a
polarization squeezed pulse with S2 the only non-zero Stokes parameter thus S1
and S3 being the conjugate pair. Polarization entanglement was generated by
interference of the polarization squeezed field with a vacuum on a 50:50 beam
splitter. The two resultant beams exhibit strong quantum noise correlations in
S1 and S3. The sum noise signal of S3 was at the respective shot noise level
and the difference noise signal of S1 fell 2.9dB below this value
Measuring entanglement of photons produced by a pulsed source
A pulsed source of entangled photons is desirable for some applications. Yet,
such a source has intrinsic problems arising from the simultaneous arrival of
the signal and noise photons to the detectors. These problems are analyzed and
practical methods to calculate the number of accidental (or spurious)
coincidences are described in detail, and experimentally checked, for the
different regimes of interest. The results are useful not only to measure
entanglement, but to all the situations where extracting the number of valid
coincidences from noisy data is required. As an example of the use of those
methods, we present the time-resolved measurement of the Concurrence of the
field produced by spontaneous parametric down conversion with pump pulses of
duration in the ns-range at a repetition of kHz. The predicted discontinuous
evolution of the entanglement at the edges of the pump pulse is observed.Comment: 9 pages, 10 or 7 figures (one of the figures includes 4), 28
Refernce
Novel Cascaded Ultra Bright Pulsed Source of Polarization Entangled Photons
A new ultra bright pulsed source of polarization entangled photons has been
realized using type-II phase matching in spontaneous parametric down conversion
process in two cascaded crystals. The optical axes of the crystals are aligned
in such a way that the extraordinarily (ordinarily) polarized cone from one
crystal overlaps with the ordinarily (extraordinarily) polarized cone from the
second crystal. This spatial overlapping removes the association between the
polarization and the output angle of the photons that exist in a single type-II
down conversion process. Hence, entanglement of photons originating from any
point on the output cones is possible if a suitable optical delay line is used.
This delay line is particularly simple and easy to implement.Comment: 8 pages 8 figure
Coherent Neutral Current Neutrino-Nucleus Scattering at a Spallation Source; a Valuable Experimental Probe
The coherent contribution of all neutrons in neutrino nucleus scattering due
to the neutral current is examined considering the Spallation Neutron Source
(SNS) as a source of neutrinos. SNS is a prolific pulsed source of electron and
muon neutrinos as well as muon antineutrinos.Comment: 15 LaTex pages, 14 figures, 3 Table
Pulsed source of spectrally uncorrelated and indistinguishable photons at telecom wavelengths
We report on the generation of indistinguishable photon pairs at telecom
wavelengths based on a type-II parametric down conversion process in a
periodically poled potassium titanyl phosphate (PPKTP) crystal. The phase
matching, pump laser characteristics and coupling geometry are optimised to
obtain spectrally uncorrelated photons with high coupling efficiencies. Four
photons are generated by a counter- propagating pump in the same crystal and
anlysed via two photon interference experiments between photons from each pair
source as well as joint spectral and g^(2) measurements. We obtain a spectral
purity of 0.91 and coupling efficiencies around 90% for all four photons
without any filtering. These pure indistinguishable photon sources at telecom
wavelengths are perfectly adapted for quantum network demonstrations and other
multi-photon protocols
1.65µm long range distributed testing of optical fibres using a compact Q-switched fibre laser
A simple Q-switched Erbium-doped fibre laser operating at 1.5µm forms the basis of a high peak power pulsed source at 1.65µm. Applications include monitoring of active telecommunication links, loss measurement at 1.65µm and distributed temperature sensing
Pulsed energy-time entangled twin-photon source for quantum communication
A pulsed source of energy-time entangled photon pairs pumped by a standard
laser diode is proposed and demonstrated. The basic states can be distinguished
by their time of arrival. This greatly simplifies the realization of 2-photon
quantum cryptography, Bell state analyzers, quantum teleportation, dense
coding, entanglement swapping, GHZ-states sources, etc. Moreover the
entanglement is well protected during photon propagation in telecom optical
fibers, opening the door to few-photon applications of quantum communication
over long distances.Comment: 8 pages, 4 figure
Photon number resolving detection using time-multiplexing
Detectors that can resolve photon number are needed in many quantum
information technologies. In order to be useful in quantum information
processing, such detectors should be simple, easy to use, and be scalable to
resolve any number of photons, as the application may require great portability
such as in quantum cryptography. Here we describe the construction of a
time-multiplexed detector, which uses a pair of standard avalanche photodiodes
operated in Geiger mode. The detection technique is analysed theoretically and
tested experimentally using a pulsed source of weak coherent light.Comment: 20 pages, 14 figures, accepted to Journal of Modern Optic
Pulsed-Source Interferometry in Acoustic Imaging
A combination of pulsed-source interferometry and acoustic diffraction has been proposed for use in imaging subsurface microscopic defects and other features in such diverse objects as integrated-circuit chips, specimens of materials, and mechanical parts. A specimen to be inspected by this technique would be mounted with its bottom side in contact with an acoustic transducer driven by a continuous-wave acoustic signal at a suitable frequency, which could be as low as a megahertz or as high as a few hundred gigahertz. The top side of the specimen would be coupled to an object that would have a flat (when not vibrating) top surface and that would serve as the acoustical analog of an optical medium (in effect, an acoustical "optic")
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