Observation and analysis of the spatial frequency response of an atomic magnetometer

An atomic magnetometer is an ultra-high-sensitivity sensor that measures magnetic fields by means of atomic spin polarization. The spatial frequency response (SFR), which describes the spin polarizations corresponding to the field at different spatial frequencies, is an important property of atomic magnetometers. To characterize the SFR, one must generate a spatially varying field with scannable spatial frequencies (in units of mm − 1), a concept that is similar to that in the time domain. However, it is much more difficult to generate a varying magnetic field spatially using traditional magnetic coils than it is to do so temporally. We generate an equivalent field B y sin ⁡ ( ξ x ) with spatial frequency ξ from 0.14 mm − 1 to 36.5 mm − 1 by modulating the pump laser beam with a digital micromirror device and then obtain the SFR of a Cs atomic magnetometer by measuring the spin polarization of Cs at different spatial frequencies. The experimentally obtained SFR agrees well with the response calculated based on the Bloch equations and Fick’s second diffusion law. We also discuss a new definition of spatial resolution that can be used to characterize and compare the background spatial resolutions of different atomic magnetometers.