47 research outputs found
A fast pneumatic sample-shuttle with attenuated shocks
We describe a home-built pneumatic shuttle suitable for the fast displacement
of samples in the vicinity of a highly sensitive atomic magnetometer. The
samples are magnetized at 1 T using a Halbach assembly of magnets. The device
enables the remote detection of free induction decay in ultra-low-field and
zero-field NMR experiments, in relaxometric measurements and in other
applications involving the displacement of magnetized samples within time
intervals as short as a few tens of milliseconds. Other possible applications
of fast sample shuttling exist in radiological studies, where samples have to
be irradiated and then analyzed in a 'cold' environment.Comment: 3 pages and 3 figures; 2 additional pages (2 figures) as a
supplemental materia
Multichannel optical atomic magnetometer operating in unshielded environment
A multi-channel atomic magnetometer operating in an unshielded environment is
described and characterised. The magnetometer is based on D1 optical pumping
and D2 polarimetry of Cs vapour contained in gas-buffered cells. Several
technical implementations are described and discussed in detail. The
demonstrated sensitivity of the setup is 100fT/Hz^1/2 when operating in the
difference mode.Comment: 9 pages, 5 figures, appearing in Appl.Phys.
Self-adaptive loop for external disturbance reduction in differential measurement set-up
We present a method developed to actively compensate common-mode magnetic
disturbances on a multi-sensor device devoted to differential measurements. The
system uses a field-programmable-gated-array card, and operates in conjunction
with a high sensitivity magnetometer: compensating the common-mode of magnetic
disturbances results in a relevant reduction of the difference-mode noise. The
digital nature of the compensation system allows for using a numerical approach
aimed at automatically adapting the feedback loop filter response. A common
mode disturbance attenuation exceeding 50 dB is achieved, resulting in a final
improvement of the differential noise floor by a factor of 10 over the whole
spectral interval of interest.Comment: 7 pages, 8 figures, 26 ref
Restoring Narrow Linewidth to a Gradient-Broadened Magnetic Resonance by Inhomogeneous Dressing
We study the possibility of counteracting the line-broadening of atomic
magnetic resonances due to inhomogeneities of the static magnetic field by
means of spatially dependent magnetic dressing, driven by an alternating field
that oscillates much faster than the Larmor precession frequency. We
demonstrate that an intrinsic resonance linewidth of 25~Hz that has been
broadened up to hundreds Hz by a magnetic field gradient, can be recovered by
the application of an appropriate inhomogeneous dressing field. The findings of
our experiments may have immediate and important implications, because they
facilitate the use of atomic magnetometers as robust, high sensitivity
detectors in ultra-low-field NMR imaging.Comment: 9 pages, 7 figures, 33 refs. This is the unedited versio
A Non-Inductive Magnetic Eye-Tracker: From Dipole Tracking to Gaze Retrieval
We analyze the information that can be retrieved from the tracking parameters produced by an innovative wearable eye tracker. The latter is based on a permanent-magnet marked corneal lens and by an array of magnetoresistive detectors that measure the magnetostatic field in several positions in the eye proximity. We demonstrate that, despite missing information due to the axial symmetry of the measured field, physiological constraints or measurement conditions make possible to infer complete eye-pose data. Angular precision and accuracy achieved with the current prototypical device are also assessed and briefly discussed. The results show that the instrumentation considered is suitable as a new, moderately invasive medical diagnostics for the characterization of ocular movements and associated disorders
Stray Magnetic Field Compensation with a Scalar Atomic Magnetometer
We describe a system for the compensation of time-dependent stray magnetic
fields using a dual channel scalar magnetometer based on non-linear Faraday
rotation in synchronously optically pumped Cs vapour. We detail the active
control strategy, with an emphasis on the electronic circuitry, based on a
simple phase-locked-loop integrated circuit. The performance and limits of the
system developed are tested and discussed. The system was applied to
significantly improve the detection of free induction decay signals from
protons of remotely magnetized water precessing in an ultra-low magnetic field.Comment: 8 pages, 6 figures, 31 refs, v2 (with minor improvements) appearing
in Rev.Sc.Instr. June 201
Microtesla NMR J-coupling spectroscopy with an unshielded atomic magnetometer
We present experimental data and theoretical interpretation of NMR spectra of
remotely magnetized samples, detected in an unshielded environment by means of
a differential atomic magnetometer. The measurements are performed in an
ultra-low-field at an intermediate regime, where the J-coupling and the Zeeman
energies have comparable values and produce rather complex line sets, which are
satisfactorily interpreted.Comment: 8 pages, 8 figs, appearing in JMR (2016
Simultaneous Detection of H and D NMR Signals in a micro-Tesla Field
We present NMR spectra of remote-magnetized deuterated water, detected in an
unshielded environment by means of a differential atomic magnetometer. The
measurements are performed in a T field, while pulsed techniques are
applied -following the sample displacement- in a 100~T field, to tip both
D and H nuclei by controllable amounts. The broadband nature of the detection
system enables simultaneous detection of the two signals and accurate
evaluation of their decay times. The outcomes of the experiment demonstrate the
potential of ultra-low-field NMR spectroscopy in important applications where
the correlation between proton and deuteron spin-spin relaxation rates as a
function of external parameters contains significant information.Comment: 7 pages (letter, 4 pages) plus supplemental material as an appendix.
This document is the unedited author's version of a Submitted Work that was
subsequently accepted for publication in Journal of Phys. Chem. Lett.,
copyright American Chemical Society after peer review. To access the final
edited and published work see:
pubs.acs.org/doi/abs/10.1021/acs.jpclett.7b0285
Spin dynamic response to a time dependent field
The dynamic response of a parametric system constituted by a spin precessing
in a time dependent magnetic field is studied by means of a perturbative
approach that unveils unexpected features, and is then experimentally
validated. The first-order analysis puts in evidence different regimes: beside
a tailorable low-pass-filter behaviour, a band-pass response with interesting
potential applications emerges. Extending the analysis to the second
perturbation order permits to study the response to generically oriented fields
and to characterize several non-linear features in the behaviour of such kind
of systems.Comment: 13 pages, 7 figures, 52 references. Accepted for publication in
Applied Physics
Sub-millimetric ultra-low-field MRI detected in situ by a dressed atomic magnetometer
Magnetic Resonance Imaging (MRI) is universally acknowledged as an excellent
tool to extract detailed spatial information with minimally invasive
measurements. Efforts toward ultra-low-field (ULF) MRI are made to simplify the
scanners and to reduce artefacts and incompatibilities. Optical Atomic
Magnetometers (OAMs) are among the sensitive magnetic detectors eligible for
ULF operation, however they are not compatible with the strong field gradients
used in MRI. We show that a magnetic-dressing technique restores the OAMs
operability despite the gradient, and we demonstrate sub-millimetric resolution
MRI with a compact experimental setup based on an in situ detection. The
proof-of-concept experiment produces unidimensional imaging of remotely
magnetized samples with a dual sensor, but the approach is suited to be adapted
for 3-D imaging of samples magnetized in loco. An extension to multi-sensor
architectures is also possible.Comment: 5 pages, 3 figures, 36 refs, 3 pages supplemental material (+ 3refs).
Accepted for publication in Appl.Phys.Let