Frequency-Dependent Amplitude Correction to Free-Precession Scalar Magnetometers

Abstract

Pump and probe scalar atomic magnetometers show incredible potential for real-world, traditionally difficult measurement environments due to their high dynamic range and linearity. Previously, it has been assumed that these scalar magnetometers have a flat response across their bandwidth and flat noise floor. Here, we show that standard fitting routines, used to extract the magnetic field, result in a nonlinear frequency dependent response across the sensor bandwidth, due to the time-averaged nature of such free precession measurements. We present an analytic correction dependent on dead-time, and show how this equation can also correct the sensor spectral density. The maximum in-band amplitude loss approaches 29% as the frequency of interest becomes the Nyquist frequency, making a significant correction for applications such as source localization in magnetoencephalography (MEG). These pump and probe atomic magnetometers are also known to have large aliasing of out-of-band signals, and we propose a scheme where the frequency of out-of-band signals can be identified by performing fits with varying dead-time on the raw free-precession sensor data.