Abstract
We demonstrate an optically pumped magnetometer (OPM) operated in a free-induction-decay (FID) configuration that is capable of tracking oscillating magnetic signals in the presence of a 50 μT static field. Excellent waveform reconstruction is demonstrated for low frequency modulations with respect to the Nyquist limited bandwidth. A 100 pT oscillation was successfully reconstructed using signal averaging, and an optimum sensitivity of 3.9 pT/Hz was measured from the spectrum of the residuals relative to the sinusoidal fit. The impact of the pump-probe repetition rate and spin depolarization on the frequency response of the sensor is investigated in detail using miniaturized vapor cell technology, with the (-3 dB) bandwidths residing beyond the Nyquist limit in each case. We also discuss technical limitations associated with the magnetometer when exposed to oscillating fields of sufficiently high amplitude or frequency. This is discussed in the context of potential distortions arising in the reproduced signals, induced by frequency modulation (FM) and aliasing artefacts.
Highlights
Pumped atomic magnetometers (OPMs) employ spin-polarized alkali-metal atoms in the vapor phase as the magnetically responsive medium
We demonstrate an optically pumped magnetometer (OPM) operated in a freeinduction-decay (FID) configuration that is capable of tracking oscillating magnetic signals in the presence of a 50 μT static field
Waveform tracking of oscillating magnetic signals was demonstrated using a magnetometer based on FID, employing a 1.5 mm thick Cs vapor cell with relaxation rates on the order of kHz
Summary
Pumped atomic magnetometers (OPMs) employ spin-polarized alkali-metal atoms in the vapor phase as the magnetically responsive medium. Nonlinearities induced by sufficiently strong time-varying magnetic signals are observed and modelled in terms of Bessel functions of the first kind We discuss this in the context of potential readout errors that can occur in the presence of prominent frequency modulation (FM) effects that introduce numerous frequency components into the FID spectrum. This increases the difficulty of frequency extraction using traditional digital signal processing (DSP) techniques such as discrete Fourier transforms (DFTs) or fitting algorithms, and places an upper limit on the sensors dynamic range with regards to AC magnetic field perturbations that can be reliably reconstructed
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