We introduce a Magnetic Particle Imaging Susceptometer (MPIS) that uses a high-sensitivity atomic magnetometer (AM) for recording the spatial distribution of fluid-suspended magnetic nanoparticles. ...We have evaluated the MPIS performance by one-dimensional scans of structured nanoparticle phantoms, demonstrating, in particular, resolutions of ≈2.5 mm prior to deconvolution and <inline-formula> <tex-math notation="LaTeX">{\ll }1 </tex-math></inline-formula> mm after deconvolution. Our instrument conceptually follows the general principle of Magnetic Particle Imaging (MPI) for encoding spatial distributions into magnetic flux density variations. Conversely to previously demonstrated MPI methods, MPIS works in time-space by recording time series of the sample's magnetic response including all Fourier components. The device deploys a specifically designed system of coils, a low-frequency excitation scheme, and a simple source localization algorithm. The difference of the AM's frequency response with respect to the conventional receive coil detection allows us to work at much lower driving frequencies. We demonstrate operation at frequencies on the order of 100 Hz, enabling the beneficial use of larger nanoparticles. The spatial distribution encoded into the particles' susceptibility needs a much lower excitation field amplitude compared to conventional MPI scanners. These two features make MPIS least harmful for biological samples and subjects compared to conventional MPI scanners. We also address performance characteristics and other possible applications of MPIS.
Laser ablation of metals in liquid helium results in the formation of metal filaments with diameters on the order of 2–10 nanometres and of spherical nanoparticles. In superfluid helium these ...nanowires aggregate into centimeter-sized networks. We study the morphology and the electric conductivity of these large aggregates, as well as extinction spectra and the crystalline structure of the individual nanofragments. We discuss the effect of superfluidity on the mechanisms of coalescence processes at the nanometer and centimeter scales.
We demonstrate optical pumping on the four hyperfine components of the Cs
D
1
transition by unpolarized (UPL) resonant laser light. The evidence is based on the reduction of the absorption ...coefficients
κ
0
with increasing light power
P
in an uncoated Cs vapor cell with isotropic spin relaxation. For comparison we perform the same quantitative
κ
0
(
P
) measurements with linearly-polarized light (LPL) and circularly-polarized light (CPL). We find that our previously published algebraic expressions give an excellent description of all experimentally recorded induced transparency signals. Based on this we can make reliable absolute predictions for the power dependence of the spin orientation and alignment produced by pumping with LPL, CPL and UPL.
Graphical abstract
We present a laser-based atomic magnetometer that allows inferring the modulus of a magnetic field from the free Larmor precession of spin-oriented Cs vapour atoms. The detection of free spin ...precession (FSP) is not subject to systematic readout errors that occur in phase feedback-controlled magnetometers in which the spin precession is actively driven by an oscillating field or a modulation of light parameters, such as frequency, amplitude, or polarization. We demonstrate that an FSP-magnetometer can achieve a ∼200 fT/√Hz sensitivity (<100 fT/√Hz in the shotnoise limit) and an absolute accuracy at the same level.
Graphical abstract
We have investigated the dependence of lock-in-demodulated
M
x
-magnetometer signals on the orientation of the static magnetic field
B
0
of interest. Magnetic resonance spectra for 2400 discrete ...orientations of
B
0
covering a
4
π
solid angle have been recorded by a PC-controlled steering and data acquisition system. Off-line fits by previously derived lineshape functions allow us to extract the relevant resonance parameters (shape, amplitude, width, and phase) and to represent their dependence on the orientation of
B
0
with respect to the laser beam propagation direction. We have performed this study for two distinct
M
x
-magnetometer configurations, in which the rf-field is either parallel or perpendicular to the light propagation direction. The results confirm well the algebraic theoretical model functions. We suggest that small discrepancies are related to hitherto uninvestigated atomic alignment contributions.
The Global Network of Optical Magnetometers for Exotic physics searches (GNOME) is a network of time-synchronized, geographically separated, optically pumped atomic magnetometers that is being used ...to search for correlated transient signals heralding exotic physics. GNOME is sensitive to exotic couplings of atomic spins to certain classes of dark matter candidates, such as axions. This work presents a data analysis procedure to search for axion dark matter in the form of topological defects: specifically, walls separating domains of discrete degenerate vacua in the axion field. An axion domain wall crossing the Earth creates a distinctive signal pattern in the network that can be distinguished from random noise. The reliability of the analysis procedure and the sensitivity of the GNOME to domain-wall crossings are studied using simulated data.
In a recent article in this journal Grewal and Pattabiraman reported on the splitting of ground state Hanle resonances (recorded with linearly polarized light) by a transverse field. They claimed a ...“linearly proportional” dependence on the transverse field strength and supported this observation with results from numerical simulations. In this comment we argue that the splitting occurs only beyond a certain threshold field value and that it has a strong non-linearity near threshold. We base this claim on our previously published algebraic expressions for the line shapes and support this by experimental evidence.
Graphical abstract
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