Triaxial Vector Operation in Near-Zero Field of Atomic Magnetometer With Femtotesla Sensitivity

Compact atomic magnetometer has become an important approach for noise measurement of magnetic shielding systems as well as biomagnetic measurement. In this study, we propose a novel method that enables time-shard triaxial magnetic field measurements in near-zero magnetic field through a compact high-performance atomic magnetometer with femtotesla sensitivity. With pump–probe orthogonal configuration, the magnetometer can be operated without optical and magnetic modulation. The
y
-axis magnetic field measurement was realized in zero field, whereas the
x
- and
z
- axes magnetic fields were measured by the cross-application of the bias magnetic fields operating in near-zero field. The maximum response amplitude and sensitivity with bandwidths of 46.8 Hz (
x
- axis), 10.5 Hz (
y
-axis), and 10.9 Hz (
z
-axis) are achieved under bias magnetic fields of
$B_{z-\mathrm {offset}}= 8$
nT and
$B_{x-\mathrm {offset}} = 2$
nT. The bandwidth along
x
- axis was extended to 232 Hz under
$B_{z-\mathrm {offset}} = 32$
nT, which can further be improved by increasing
$B_{z-\mathrm {offset}}$
. The linear interval of measurable magnetic field are between −11.7 to +11.7 nT (
x
- axis), −0.8 to +0.8 nT (
y
-axis), and −28.2 to +28.2 nT (
z
-axis). For
x
- and
z
-axes, the measurable interval can further be improved by increasing
$B_{z-\mathrm {offset}}$
and
$B_{x-\mathrm {offset}}$
, respectively. The triaxial sensitivities achieved through our method reached 3.1 ± 0.3 fT/Hz
^1/2
(
x
- axis), 2.0 ± 0.1 fT/Hz
^1/2
(
y
- axis), and 6.0 ± 0.5 fT/Hz
^1/2
(
z
- axis). This system is measured in a low-noise ferrite magnetic shield to ensure extra-low magnetic noise condition. Furthermore, the non-modulation triaxial vector operation demonstrated in this study is advantageous for reducing interference and spin-exchange relaxation caused by magnetic field modulation.