# Vector Magnetometry Exploiting Phase-Geometry Effects in a Double-Resonance Alignment Magnetometer

## TL;DR

This paper introduces a novel method using phase-geometry effects in a double-resonance alignment magnetometer to simultaneously measure the magnitude and orientation of static magnetic fields with high precision.

## Contribution

It demonstrates for the first time that phase and amplitude of harmonic signals can be used for vector magnetometry in a double-resonance system.

## Key findings

- Achieved 1.7 pT sensitivity in static field magnitude
- Measured field orientation with 0.63 mrad resolution
- Validated theoretical model with experimental data

## Abstract

Double-resonance optically pumped magnetometers are an attractive instrument for unshielded magnetic field measurements due to their wide dynamic range and high sensitivity. Use of linearly polarised pump light creates alignment in the atomic sample, which evolves in the local static magnetic field, and is driven by a resonant applied field perturbation, modulating the polarisation of transmitted light. We show for the first time that the amplitude and phase of observed first- and second-harmonic components in the transmitted polarisation signal contain sufficient information to measure static magnetic field magnitude and orientation. We describe a laboratory system for experimental measurements of these effects and verify a theoretical derivation of the observed signal. We demonstrate vector field tracking under varying static field orientations and show that the static field magnitude and orientation may be observed simultaneously, with experimentally realised resolution of 1.7 pT and 0.63 mrad in the most sensitive field orientation.