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Magnetometry using hot atomic vapors

Martín Romero, Fernando

Published Jul 19, 2022• 0 citations
OpenAlex

Abstract

We demonstrate an ultra-high sensitivity rf optical magnetometer based on a compact 5×5×8 mm3 Rubidium-87 vapor cell in a mu-metal shielded environment. The rf field is detected via a Faraday rotation effect on the linear polarization of a probe beam, and the resonance frequency is tuned via Zeeman effect by applying a static bias magnetic field to the cell. Sensitivities down to 3 fT/√Hz are achieved between 10 kHz and 100 kHz, which is a performance comparable to that of prior larger cells. An increase in the sensitivity with frequency and temperature has been observed.

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We demonstrate an ultra-high sensitivity rf optical magnetometer based on a compact 5×5×8 mm3 Rubidium-87 vapor cell in a mu-metal shielded environment. The rf field is detected via a Faraday rotation effect on the linear polarization of a probe beam, and the resonance frequency is tuned via Zeeman effect by applying a static bias magnetic field to the cell. Sensitivities down to 3 fT/√Hz are achieved between 10 kHz and 100 kHz, which is a performance comparable to that of prior larger cells. An increase in the sensitivity with frequency and temperature has been observed.
We describe an alkali-metal magnetometer for detection of weak magnetic fields in the radio-frequency (rf) range. High sensitivity is achieved by tuning the Zeeman resonance of alkali atoms to the rf frequency and partially suppressing spin-exchange collisions in the alkali-metal vapor. We demonstrate magnetic field sensitivity of 2 fT/Hz(1/2) at a frequency of 99 kHz with a resonance width of 400 Hz. We also derive a simple analytic expression for the fundamental limit on the sensitivity of the rf magnetometer and show that a sensitivity of about 0.01 fT/Hz(1/2) can be achieved in a practical system with a measurement volume of 200 cm3.
A high-sensitivity optically pumped atomic magnetometer working in the geomagnetic range utilizing the light-narrowing effect and in-phase excitation is described. The setup is based on a simple pump–probe arrangement built around a Cs vapor cell whose active volume is 64 mm3. The transverse oscillating field is applied parallel to the probe beam to drive Zeeman resonance, and the in-phase component of the resonance signal is measured to determine the field. The sensitivity of the magnetometer is improved by pumping most atoms into the stretched state. Consequently, spin-exchange relaxation is suppressed, and a sensitivity of 0.1 pT/Hz1/2 in the range of 10 μT is achieved. This magnetometer has the advantages of large dynamic range, high performance of low-frequency stabilization, high response speed, and compact size. It can be used for many cutting-edge applications such as detection of magnetic anomalies.
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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.
We demonstrate the nonlinear magnetoelectric (ME) effect in atomic vapor achieved through the parametric interaction of optical electric and radio-frequency (rf) magnetic fields leading to the generation of new optical electric fields. Density matrix calculations are performed to validate the experimental results. Moreover, the predicted dependence of the generated optical electric field amplitudes on the rf magnetic field strength is experimentally verified to confirm the ME effect. The system provides a technique for precision rf magnetometry based on this phenomenon. We could experimentally achieve an rf magnetic field sensitivity of 70 fT/Hz\mathrm{fT}/\sqrt{\text{Hz}}fT/Hz​ at 1 kHz to 7.5 pT/Hz\mathrm{pT}/\sqrt{\text{Hz}}pT/Hz​ at 3 MHz for zero bias field in an unshielded environment. The appealing features of the proposed rf magnetometer using our system include a high dynamic range up to 1012{10}^{12}1012, 6 dB bandwidth of 450 kHz, and arbitrary frequency resolution, which are intrinsic to the nonlinear ME effect in the medium.
We describe an optically pumped 87Rb magnetometer with 5 fT/Hz(1/2) sensitivity when operated in the spin-exchange relaxation free (SERF) regime. The magnetometer uses a microfabricated vapor cell consisting of a cavity etched in a 1 mm thick silicon wafer with anodically bonded Pyrex windows. The measurement volume of the magnetometer is 1 mm3, defined by the overlap region of a circularly polarized pump laser and a linearly polarized probe laser, both operated near 795 nm. Sensitivity limitations unique to the use of microfabricated cells are discussed.