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arXiv:2209.04249 · Physical Review Applied

Single-Beam Room-Temperature Atomic Magnetometer with Large Bandwidth and Dynamic Range

K. K. George Kurian, Sushree S. Sahoo, Perunthiruthy K. Madhu, G Rajalakshmi

Published May 11, 2023• 13 citations
arXivHTMLPDF

Abstract

We present a single-beam atomic magnetometer operating at room temperature for the measurement of ac magnetic fields. The magnetometer functions in the nonlinear regime of magneto-optical rotation of ${}^{85}\mathrm{Rb}$ atomic vapor without any buffer gases. We demonstrate a sensitivity of approximately $0.9\phantom{\rule{0.2em}{0ex}}\mathrm{pT}/\sqrt{\mathrm{Hz}}$ at 2 kHz and a large bandwidth of 24 kHz. The dynamic range of measurement is ${10}^{6}$, making the sensor effective even in Earth's field. We present the signal-to-noise and bandwidth characteristics of the system for both shielded and unshielded modes of operation. Moreover, we perform theoretical analysis for the atom-light system for the single-laser-beam configuration. The effect of light intensity and detuning on the magnetometer is studied theoretically as well as experimentally to understand the strengths and limitations of the technique.

DOI
10.1103/physrevapplied.19.054040

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We present a single-beam atomic magnetometer operating at room temperature for the measurement of ac magnetic fields. The magnetometer functions in the nonlinear regime of magneto-optical rotation of 85Rb{}^{85}\mathrm{Rb}85Rb atomic vapor without any buffer gases. We demonstrate a sensitivity of approximately 0.9pT/Hz0.9\phantom{\rule{0.2em}{0ex}}\mathrm{pT}/\sqrt{\mathrm{Hz}}0.9pT/Hz​ at 2 kHz and a large bandwidth of 24 kHz. The dynamic range of measurement is 106{10}^{6}106, making the sensor effective even in Earth's field. We present the signal-to-noise and bandwidth characteristics of the system for both shielded and unshielded modes of operation. Moreover, we perform theoretical analysis for the atom-light system for the single-laser-beam configuration. The effect of light intensity and detuning on the magnetometer is studied theoretically as well as experimentally to understand the strengths and limitations of the technique.
Abstract We demonstrate a dual-beam high-sensitivity room-temperature atomic magnetometer (AM) with a large dynamic range based on a nonlinear magneto-optical rotation (NMOR) enhancing scheme. Using an inelastic wave-mixing laser, we find significant NMOR signal enhancement compared with a single-beam scheme under the same far-detuned operation conditions. This dual-beam scheme is shown to operate well in the regime of lower laser intensity and off-resonance detuning. The best sensitivity achieved is 20 fT/Hz1/2 with a bandwidth of 2 kHz, substantially greater than common spin-exchange relaxation-free AMs. This provides a way to develop low-power, inexpensive miniaturized AMs for wide application.
We report on a single-channel rubidium radio-frequency atomic magnetometer operating in unshielded \nenvironments and near room temperature with a measured sensitivity of 130 fT/√ \nHz. We demonstrate \nconsistent, narrow-bandwidth operation across the kHz–MHz band, corresponding to three orders \nof magnitude of the magnetic field amplitude. A compensation coil system controlled by a feedback \nloop actively and automatically stabilizes the magnetic field around the sensor. We measure \na reduction in the 50 Hz noise contribution by an order of magnitude. The small effective sensor \nvolume, 57 mm3 \n, increases the spatial resolution of the measurements. Low temperature operation, \nwithout any magnetic shielding, coupled with the broad tunability, and low beam power, dramatically \nextends the range of potential field applications for our device.
Here we demonstrate an atomic magnetometer that has a bandwidth of more than 100 kHz and a sensitivity of $180\phantom{\rule{0.2em}{0ex}}\mathrm{fT/}\ensuremath{\surd}\mathrm{Hz}$ at a Fourier frequency of 8 Hz, and $0.7\phantom{\rule{0.2em}{0ex}}\mathrm{nT/}\ensuremath{\surd}\mathrm{Hz}$ at 100 kHz. These sensitivity measurements are achieved at geophysically useful magnetic field magnitudes (approximately $50\phantom{\rule{0.2em}{0ex}}\ensuremath{\mu}\mathrm{T}$ inside a three-layer $\ensuremath{\mu}$-metal shield) and are limited by the photon shot noise for frequencies above 8 Hz. This device is based on a nonlinear magneto-optical rotation sensor that is operated with an active feedback to the pump modulation frequency. We present a theoretical description of the response functions of the components in the magnetometer. We show that the range of operation of atomic magnetometers can thus be expanded beyond the conventional high-sensitivity, low-bandwidth domain, to provide a high-linearity, high-bandwidth, and high-sensitivity sensor.
We report on a single-channel rubidium radio-frequency atomic magnetometer operating in unshielded environments and near room temperature with a measured sensitivity of 130 fT/Hz. We demonstrate consistent, narrow-bandwidth operation across the kHz–MHz band, corresponding to three orders of magnitude of the magnetic field amplitude. A compensation coil system controlled by a feedback loop actively and automatically stabilizes the magnetic field around the sensor. We measure a reduction in the 50 Hz noise contribution by an order of magnitude. The small effective sensor volume, 57 mm3, increases the spatial resolution of the measurements. Low temperature operation, without any magnetic shielding, coupled with the broad tunability, and low beam power, dramatically extends the range of potential field applications for our device.
We introduce a new ultra-sensitive adiabatic magnetometer that has a broad bandwidth and can operate in the presence of magnetic fields and gradients. It follows conceptually typical implementations of atomic magnetometers based on alkali-metal vapor cells and lasers for optical pumping and optical Faraday effect detection, while its unique feature is a measurement of an oscillating magnetic field along the probe beam direction at frequencies lower than the resonant frequency, proportional to a static magnetic field along the pump beam direction. The bandwidth of the adiabatic magnetometer scales as the strength of the field along the pump beam. From our theoretical studies it is expected that the adiabatic magnetometer can reach 1 fT sensitivity with a bandwidth of 10 kHz, which any type of atomic magnetometers cannot achieve. Among anticipated various applications of this adiabatic magnetometer are biomagnetic sensing, nuclear magnetic resonance detection, and alkali-metal density measurements. We experimentally conducted alkali-metal density measurements, as an example of applications.
A self-oscillating magnetometer based on nonlinear magneto-optical rotation using amplitude-modulated pump light and unmodulated probe light (AM-NMOR) in 87Rb has been constructed and tested towards a goal of airborne detection of magnetic anomalies. In AM-NMOR, stroboscopic optical pumping via amplitude modulation of the pump beam creates alignment of the ground electronic state of the rubidium atoms. The Larmor precession causes an ac rotation of the polarization of a separate probe beam; the polarization rotation frequency provides a measure of the magnetic field. An anti-relaxation coating on the walls of the atomic vapor cell results in a long lifetime of 56 ms for the alignment, which enables precise measurement of the precession frequency. Light is delivered to the magnetometer by polarization-maintaining optical fibers. Tests of the sensitivity include directly measuring the beat frequency between the magnetometer and a commercial instrument and measurements of Earth's field under magnetically quiet conditions, indicating a sensitivity of at least 5 pT/νHz. Rotating the sensor indicates a heading error of less than 1 nT, limited in part by residual magnetism of the sensor.