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Optics Express

Characteristics and performance of an intensity-modulated optically pumped magnetometer in comparison to the classical M_x magnetometer

V. Schultze, R.P.J. IJsselsteijn, Theo Scholtes, Stefan Woetzel, Hans‐Georg Meyer

Published Jun 11, 2012• 51 citations
Publisher

Abstract

We compare the performance of two methods for the synchronization of the atomic spins in optically pumped magnetometers: intensity modulation of the pump light and the classical M(x) method using B(1) field modulation. Both techniques use the same set-up and measure the resulting features of the light after passing a micro-fabricated Cs cell. The intensity-modulated pumping shows several advantages: better noise-limited magnetic field sensitivity, misalignment between pumping and spin synchronization is excluded, and magnetometer arrays without any cross-talk can be easily set up.

DOI
10.1364/oe.20.014201

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We compare the performance of two methods for the synchronization of the atomic spins in optically pumped magnetometers: intensity modulation of the pump light and the classical M(x) method using B(1) field modulation. Both techniques use the same set-up and measure the resulting features of the light after passing a micro-fabricated Cs cell. The intensity-modulated pumping shows several advantages: better noise-limited magnetic field sensitivity, misalignment between pumping and spin synchronization is excluded, and magnetometer arrays without any cross-talk can be easily set up.
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Resonant excitation of an atomic medium with amplitude modulated (AM) light can produce synchronous optical pumping effects. Nonlinear magneto-optical rotation (NMOR) is produced with AM light when the optical pumping rate is synchronous with the Larmor frequency. Traditionally, magnetic field measurements have been performed using lock-in detection of the NMOR signal with the transmitted light. Instead of NMOR, we have studied intensity correlation between two orthogonally polarized components of the AM light passing through a rubidium vapor cell, for magnetic field measurements. We have used a pure 87Rb cell (1 cm in diameter and 2 cm in length) filled with Ne buffer gas for this study. Intensity correlation is performed by recording the intensity data from two fast photodetectors with a high bandwidth digitizer board. We have measured the dependence of the zero-delay intensity correlation on the magnetic field. We have also studied the dependence of the correlation width on the light intensity and cell temperature. Results obtained from the theoretical model are also compared with the experiment. The results suggest intensity correlation can be used as a viable technique for improving the performance of magnetic field measurements with AM light.
We demonstrate an optically pumped (87)Rb magnetometer in a microfabricated vapor cell based on a zero-field dispersive resonance generated by optical modulation of the (87)Rb ground state energy levels. The magnetometer is operated in the spin-exchange relaxation-free regime where high magnetic field sensitivities can be achieved. This device can be useful in applications requiring array-based magnetometers where radio frequency magnetic fields can induce cross-talk among adjacent sensors or affect the source of the magnetic field being measured.
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We compare the sensitivity performance of two optically pumped atomic magnetometers based on the Mx and frequency-modulated bell-bloom configurations. The Cs magnetometers are implemented using a millimeter-scale microfabricated vapor cell. It is found that the Bell-Bloom magnetometer yields sensitivities similar to those of the Mx magnetometer when operated under equally optimized conditions. The Bell-Bloom approach offers several attractive features over the Mx approach for chip-scale magnetometer instrumentation.