Quantum magnetometry with OPM: Novel applications in non-destructive testing?

Microfabricated optically pumped magnetometers (OPM) are a novel class of commercially available quantum magnetometers combining high sensitivity with high dynamic range. In non-destructive testing (NDT) this should enable new applications like measuring stray fields arising from small stress concentrations affecting local magnetization. In ferromagnetic steel the sensitivity of OPM is sufficient to measure magnetization from critical stresses for crack initiation in submillimeter volumes. However, OPM, as they are built today, require additional components like magnetic flux guides to control the measurement volume in NDT systems. The improvement of spatial resolution with such a flux guide is demonstrated using neighbored weld seams as an example for stress concentrations.