258 research outputs found
Magnetic-field-dependent photodynamics of single NV defects in diamond: Application to qualitative all-optical magnetic imaging
Magnetometry and magnetic imaging with nitrogen-vacancy (NV) defects in
diamond rely on the optical detection of electron spin resonance (ESR).
However, this technique is inherently limited to magnetic fields that are weak
enough to avoid electron spin mixing. Here we focus on the high off-axis
magnetic field regime for which spin mixing alters the NV defect spin dynamics.
We first study in a quantitative manner the dependence of the NV defect optical
properties on the magnetic field vector B. Magnetic-field-dependent
time-resolved photoluminescence (PL) measurements are compared to a seven-level
model of the NV defect that accounts for field-induced spin mixing. The model
reproduces the decreases in (i) ESR contrast, (ii) PL intensity and (iii)
excited level lifetime with an increasing off-axis magnetic field. We next
demonstrate that those effects can be used to perform all-optical magnetic
imaging in the high off-axis magnetic field regime. Using a scanning NV defect
microscope, we map the stray field of a magnetic hard disk through both PL and
fluorescence lifetime imaging. This all-optical method for high magnetic field
imaging at the nanoscale might be of interest in the field of nanomagnetism,
where samples producing fields in excess of several tens of milliteslas are
typical
Magnetic imaging with an ensemble of Nitrogen Vacancy centers in diamond
The nitrogen-vacancy (NV) color center in diamond is an atom-like system in
the solid-state which specific spin properties can be efficiently used as a
sensitive magnetic sensor. An external magnetic field induces Zeeman shifts of
the NV center levels which can be measured using Optically Detected Magnetic
Resonance (ODMR). In this work, we exploit the ODMR signal of an ensemble of NV
centers in order to quantitatively map the vectorial structure of a magnetic
field produced by a sample close to the surface of a CVD diamond hosting a thin
layer of NV centers. The reconstruction of the magnetic field is based on a
maximum-likelihood technique which exploits the response of the four intrinsic
orientations of the NV center inside the diamond lattice. The sensitivity
associated to a 1 {\mu}m^2 area of the doped layer, equivalent to a sensor
consisting of approximately 10^4 NV centers, is of the order of 2
{\mu}T/sqrt{Hz}. The spatial resolution of the imaging device is 400 nm,
limited by the numerical aperture of the optical microscope which is used to
collect the photoluminescence of the NV layer. The versatility of the sensor is
illustrated by the accurate reconstruction of the magnetic field created by a
DC current inside a copper wire deposited on the diamond sample.Comment: 11 pages, 5 figures, figure 4 added, results unchange
Wide bandwidth instantaneous radio frequency spectrum analyzer based on nitrogen vacancy centers in diamond
We propose an original analog method to perform instantaneous and quantitative spectral analysis
of microwave signals. An ensemble of nitrogen-vacancy (NV) centers held in a diamond plate is
pumped by a 532 nm laser. Its photoluminescence is imaged through an optical microscope and
monitored by a digital camera. An incoming microwave signal is converted into a microwave field
in the area of the NV centers by a loop shaped antenna. The resonances induced by the magnetic
component of that field are detected through a decrease of the NV centers photoluminescence. A
magnetic field gradient induces a Zeeman shift of the resonances and transforms the frequency information
into spatial information, which allows for the simultaneous analysis of the microwave
signal in the entire frequency bandwidth of the device. The time dependent spectral analysis of an
amplitude modulated microwave signal is demonstrated over a bandwidth of 600 MHz, associated
to a frequency resolution of 7MHz , and a refresh rate of 4 ms. With such integration time, a field
of a few hundreds of lW can be detected. Since the optical properties of NV centers can be
maintained even in high magnetic field, we estimate that an optimized device could allow
frequency analysis in a range of 30 GHz, only limited by the amplitude of the magnetic field
gradient. In addition, an increase of the NV centers quantity could lead both to an increase of the
microwave sensitivity and to a decrease of the minimum refresh rate down to a few ls
Hard X-ray polarimetry with Caliste, a high performance CdTe based imaging spectrometer
Since the initial exploration of soft gamma-ray sky in the 60's, high-energy
celestial sources have been mainly characterized through imaging, spectroscopy
and timing analysis. Despite tremendous progress in the field, the radiation
mechanisms at work in sources such as neutrons stars and black holes are still
unclear. The polarization state of the radiation is an observational parameter
which brings key additional information about the physical process. This is why
most of the projects for the next generation of space missions covering the
tens of keV to the MeV region require a polarization measurement capability. A
key element enabling this capability is a detector system allowing the
identification and characterization of Compton interactions as they are the
main process at play. The hard X-ray imaging spectrometer module, developed in
CEA with the generic name of Caliste module, is such a detector. In this paper,
we present experimental results for two types of Caliste-256 modules, one based
on a CdTe crystal, the other one on a CdZnTe crystal, which have been exposed
to linearly polarized beams at the European Synchrotron Radiation Facility.
These results, obtained at 200-300 keV, demonstrate their capability to give an
accurate determination of the polarization parameters (polarization angle and
fraction) of the incoming beam. Applying a selection to our data set,
equivalent to select 90 degrees Compton scattered interactions in the detector
plane, we find a modulation factor Q of 0.78. The polarization angle and
fraction are derived with accuracies of approximately 1 degree and 5%. The
modulation factor remains larger than 0.4 when essentially no selection is made
at all on the data. These results prove that the Caliste-256 modules have
performances allowing them to be excellent candidates as detectors with
polarimetric capabilities, in particular for future space missions.Comment: 17 pages, 14 figures, 2 tables in Experimental Astronomy, 201
A photon calorimeter using lead tungstate crystals for the CEBAF Hall A Compton polarimeter
The performances of the calorimeter of the Jlab Hall A Compton Polarimeter
have been measured using the Mainz tagged photon beam.Comment: 13 page
Fast-neutron induced background in LaBr3:Ce detectors
The response of a scintillation detector with a cylindrical 1.5-inch LaBr3:Ce
crystal to incident neutrons has been measured in the energy range En = 2-12
MeV. Neutrons were produced by proton irradiation of a Li target at Ep = 5-14.6
MeV with pulsed proton beams. Using the time-of-flight information between
target and detector, energy spectra of the LaBr3:Ce detector resulting from
fast neutron interactions have been obtained at 4 different neutron energies.
Neutron-induced gamma rays emitted by the LaBr3:Ce crystal were also measured
in a nearby Ge detector at the lowest proton beam energy. In addition, we
obtained data for neutron irradiation of a large-volume high-purity Ge detector
and of a NE-213 liquid scintillator detector, both serving as monitor detectors
in the experiment. Monte-Carlo type simulations for neutron interactions in the
liquid scintillator, the Ge and LaBr3:Ce crystals have been performed and
compared with measured data. Good agreement being obtained with the data, we
present the results of simulations to predict the response of LaBr3:Ce
detectors for a range of crystal sizes to neutron irradiation in the energy
range En = 0.5-10 MeVComment: 28 pages, 10 figures, 4 Table
Unusual consequences of status epilepticus in Dravet syndrome
AbstractAlthough status epilepticus (SE) affects the course of Dravet syndrome (DS), it rarely alters dramatically psychomotor outcome. We report an unusual pattern in 3 patients who following refractory SE lasting respectively 2, 7 and 12h experienced persistent and severe cognitive and motor deterioration. We compared these patients to published data and to personal experience in Necker hospital, to find links between severe outcome and clinical features such as treatment or duration of refractory SE. The key point was that anoxoischemic-like lesions appeared on MRI although cardiovascular function had remained stable. Therefore, neither hemodynamic failure, nor abnormalities of cardiac rhythm could explain the lesions and neurological worsening. For theoretical reasons the responsibility of therapy common for the 3 patients, e.g., barbiturates was suspected
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