Pulsed operation of a miniature scalar optically pumped magnetometer

Abstract

A scalar magnetic field sensor based on a millimeter-size 87Rb vapor cell is described. The magnetometer uses nearly copropagating pump and probe laser beams, amplitude modulation of the pump beam, and detection through monitoring the polarization rotation of the detuned probe beam. The circularly polarized pump laser resonantly drives a spin precession in the alkali atoms at the Larmor frequency. A modulation signal on the probe laser polarization is detected with a lock-in amplifier. Since the Larmor precession is driven all-optically, potential cross talk between sensors is minimized. And since the pump light is turned off during most of the precession cycle, large offsets of the resonance, typically present in a single-beam Bell–Bloom scheme, are avoided. At the same time, relatively high sensitivities can be reached even in millimeter-size vapor cells: The magnetometer achieves a sensitivity of 1 pT/Hz1/2 in a sensitive volume of 16 mm3, limited by environmental noise. When a gradiometer configuration is used to cancel the environmental noise, the magnetometer sensitivity reaches 300 fT/Hz1/2. We systematically study the dependence of the magnetometer performance on the optical duty cycles of the pump light and find that better performance is achieved with shorter duty cycles, with the highest values measured at 1.25% duty cycle.

Magnetic Source Imaging Using a Pulsed Optically Pumped Magnetometer Array

“…Larger fields are typically measured with OPMs by using a scalar magnetometer technique, e.g. an M x [30] or Bell-Bloom [31,32] configuration. However, for our array these configurations are not appropriate due to the large gradients across the array (~ 400 nT in the applied bias field).…”

Self-Adaptive Loop for External-Disturbance Reduction in a Differential Measurement Setup

“…These methodologies can be roughly categorized in three families: shielding, compensation, and cancellation by difference [11][12][13] . In the first two cases the external noise is reduced before the measurement, while in the third one it is measured and subsequently subtracted.…”

Free-Induction-Decay Magnetometer Based on a Microfabricated Cs Vapor Cell

“…Although sensitive, these vector sensors operate near zero field at high atomic densities, limiting the dynamic range and elevating the power required to heat the vapor cell. In contrast, total field sensors including the FID, Bell-Bloom and M x implementations have a relatively large dynamic range enabling operation in Earth-field conditions with typical * dominic.hunter@strath.ac.uk sensitivities at the pT/ √ Hz level depending on the vapor cell dimensions [8,12].…”

“…An alternative approach is to utilize synchronous optical pumping whereby the light-field is modulated at the Larmor frequency as adopted by Bell and Bloom [2]. A sensitivity of 1 pT/ √ Hz has been shown with an all-optical Bell-Bloom magnetometer using independent pump and probe beams in a sensing volume of 16 mm 3 [12].…”