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IDEA for Restoring Narrow Linewidth of a Gradient-Broadened Magnetic Resonance by Inhomogeneous Dressing.

G. Bevilacqua, V. Biancalana, Yordanka V. Dancheva, Antonio Vigilante

Published Jul 3, 2018• 0 citations
OpenAlex

Abstract

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 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.

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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 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.
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We present a theoretical study of optical magnetic-resonance imaging (OMRI), an extension of magnetic-resonance imaging to the optical frequency domain. OMRI images the spatial distribution of centers with field-dependent optical transitions by projection reconstruction from multiple tomographic scans. Spatial resolution is limited by magnetic-field gradient strengths and transition linewidths. These restrict the choice of systems accessible to OMRI, and rare-earth ions are identified as possible candidates. High-resolution laser spectroscopic techniques that overcome the effect of inhomogeneous broadening of electronic transitions are discussed. OMRI by transient hole-burning spectroscopy is presented as one approach for subwavelength spatial imaging, and its sensitivity is calculated. Submicrometer spatial resolution is possible by employing very-high-field gradients (>10 T/cm) and centers exhibiting megahertz linewidths.
We have performed high-precision experimental measurements of spin precession using a dressed 3{}^{3}3He atomic beam. Spin dressing uses an oscillating magnetic field that is both detuned to high frequency and orthogonal to a static magnetic field to effectively change the gyromagnetic ratio of a spin. We verify the validity of the spin-dressing Hamiltonian in regions beyond the limiting solution in which the Larmor frequency is much smaller than the frequency of the dressing field. We also evaluate the effect of magnetic field misalignment, i.e. if the oscillating magnetic field is not orthogonal to the static magnetic field. Modulation of the dressing-field parameters is also discussed, with a focus on whether such a modulation can be approximated merely as a time-dependent, dressed gyromagnetic ratio. Furthermore, we discuss implications for a proposed search for the neutron electric dipole moment, which would employ spin dressing to make the effective 3{}^{3}3He and neutron magnetic moments equal.
The magnetic-resonance lines of alkali atoms are broadened considerably by the spin-exchange collisions for a radio-frequency magnetometer operating at high temperature. The resonance linewidths of cesium atoms are derived by solving the relaxation equations. When spin-exchange relaxation dominates, a light narrowing effect is predicted. For the cesium atomic radio-frequency magnetometer operates at high temperature, a remarkable narrowing of the cesium magnetic-resonance lines are observed by increasing the pump power. The Cs-Cs spin-exchange relaxation is partially suppressed by light narrowing. This study helps to expand the applications of radio-frequency magnetometers in the high-sensitivity radio-frequency magnetic-field detection.
A high-sensitivity atomic magnetometer based on broad linewidth laser pumping is demonstrated. The broad linewidth laser was obtained by broadening a narrow linewidth laser utilizing an external phase modulator driven by a pseudo-random-bit-sequence (PRBS) waveform. This ingenious optical pumping scheme can significantly enhance the signal response and suppress light shift noise, as well as can reduce the gradient of electron spin polarization and improve the stability of magnetometers. Compared with a narrow linewidth laser pumping scheme, the response of the magnetometer is increased by 56%, experimentally. The relative polarization gradient is reduced from 9.8%/cm to better than 4%/cm by setting PRBS with a bit rate of 16 GHz. This scheme can also be applied to many other fields such as noninvasive bio-magnetic imaging and atomic spin gyroscopes.
We demonstrate that spin-exchange dephasing of Larmor precession at near-Earth-scale fields is effectively eliminated by dressing the alkali-metal atom spins in a sequence of ac-coupled 2π pulses, repeated at the Larmor precession frequency. The contribution of spin-exchange collisions to the spectroscopic linewidth is reduced by a factor of the duty cycle of the pulses. We experimentally demonstrate resonant transverse pumping in magnetic fields as high as 0.1 G, present experimental measurements of the suppressed spin-exchange relaxation, and show enhanced magnetometer response relative to a light-narrowed scalar magnetometer.