380 research outputs found
Low energy recoil detection with a spherical proportional counter
We present low energy recoil detection results in the keV energy region, from
measurements performed with the Spherical Proportional Counter (SPC). An
fast neutron source is used in order to obtain
neutron-nucleus elastic scattering events inside the gaseous volume of the
detector. The detector performance in the energy region was resolved by
observing the line of a X-ray source, with energy
resolution of (). The toolkit GEANT4 was used to simulate the
irradiation of the detector by an source, while SRIM
was used to calculate the Ionization Quenching Factor (IQF). The GEANT4
simulated energy deposition spectrum in addition with the SRIM calculated
quenching factor provide valuable insight to the experimental results. The
performance of the SPC in low energy recoil detection makes the detector a good
candidate for a wide range of applications, including Supernova or reactor
neutrino detection and Dark Matter (WIMP) searches (via coherent elastic
scattering).Comment: 16 pages, 16 figures, preprin
Oriented polaritons in strongly-coupled asymmetric double quantum well microcavities
Replacing independent single quantum wells inside a strongly-coupled
semiconductor microcavity with double quantum wells produces a special type of
polariton. Using asymmetric double quantum wells in devices processed into
mesas allows the alignment of the electron levels to be voltage-tuned. At the
resonant electronic tunnelling condition, we demonstrate that `oriented
polaritons' are formed, which possess greatly enhanced dipole moments. Since
the polariton-polariton scattering rate depends on this dipole moment, such
devices could reach polariton lasing, condensation and optical nonlinearities
at much lower threshold powers.Comment: 3 figure
Bragg Polaritons: Strong Coupling and Amplification in an Unfolded Microcavity
Periodic incorporation of quantum wells inside a one--dimensional Bragg
structure is shown to enhance coherent coupling of excitons to the
electromagnetic Bloch waves. We demonstrate strong coupling of quantum well
excitons to photonic crystal Bragg modes at the edge of the photonic bandgap,
which gives rise to mixed Bragg polariton eigenstates. The resulting Bragg
polariton branches are in good agreement with the theory and allow
demonstration of Bragg polariton parametric amplification.Comment: 4 pages, 4 figure
Neutron spectroscopy with the Spherical Proportional Counter
A novel large volume spherical proportional counter, recently developed, is
used for neutron measurements. Gas mixtures of with and
pure are studied for thermal and fast neutron detection, providing a
new way for the neutron spectroscopy. The neutrons are detected via the
and reactions. Here we
provide studies of the optimum gas mixture, the gas pressure and the most
appropriate high voltage supply on the sensor of the detector in order to
achieve the maximum amplification and better resolution. The detector is tested
for thermal and fast neutrons detection with a and a
neutron source. The atmospheric neutrons are successfully
measured from thermal up to several MeV, well separated from the cosmic ray
background. A comparison of the spherical proportional counter with the current
available neutron counters is also given.Comment: 7 pages, 10 figure
Ultra low energy results and their impact to dark matter and low energy neutrino physics
We present ultra low energy results taken with the novel Spherical
Proportional Counter. The energy threshold has been pushed down to about 25 eV
and single electrons are clearly collected and detected. To reach such
performance low energy calibration systems have been successfully developed: -
A pulsed UV lamp extracting photoelectrons from the inner surface of the
detector - Various radioactive sources allowing low energy peaks through
fluorescence processes. The bench mark result is the observation of a well
resolved peak at 270 eV due to carbon fluorescence which is unique performance
for such large-massive detector. It opens a new window in dark matter and low
energy neutrino search and may allow detection of neutrinos from a nuclear
reactor or from supernova via neutrino-nucleus elastic scatteringComment: 14 pages,16 figure
Optical control of spin textures in quasi-one-dimensional polariton condensates
We investigate, through polarization-resolved spectroscopy, the spin
transport by propagating polariton condensates in a quasi one-dimensional
microcavity ridge along macroscopic distances. Under circularly polarized,
continuous-wave, non-resonant excitation, a sinusoidal precession of the spin
in real space is observed, whose phase depends on the emission energy. The
experiments are compared with simulations of the spinor-polariton condensate
dynamics based on a generalized Gross-Pitaevskii equation, modified to account
for incoherent pumping, decay and energy relaxation within the condensate.Comment: 10 pages, 9 figure
Polariton Condensate Transistor Switch
A polariton condensate transistor switch is realized through optical
excitation of a microcavity ridge with two beams. The ballistically ejected
polaritons from a condensate formed at the source are gated using the 20 times
weaker second beam to switch on and off the flux of polaritons. In the absence
of the gate beam the small built-in detuning creates potential landscape in
which ejected polaritons are channelled toward the end of the ridge where they
condense. The low loss photon-like propagation combined with strong
nonlinearities associated with their excitonic component makes polariton based
transistors particularly attractive for the implementation of all-optical
integrated circuits
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