A compact, portable device for microscopic magnetic imaging based on diamond quantum sensors

Magnetic imaging based on ensembles of diamond nitrogen-vacancy quantum sensors has emerged as a useful technique for the spatial characterisation of magnetic materials and current distributions. However, demonstrations have so far been restricted to laboratory-based experiments using relatively bulky apparatus and requiring manual handling of the diamond sensing element, hampering broader adoption of the technique. Here we present a simple, compact device that can be deployed outside a laboratory environment and enables robust, simplified operation. It relies on a specially designed sensor head that directly integrates the diamond sensor while incorporating a microwave antenna and all necessary optical components. This integrated sensor head is complemented by a small control unit and a laptop computer that displays the resulting magnetic image. We test the device by imaging a magnetic sample, demonstrating a spatial resolution of 4 $\mu$m over a field of view exceeding 1 mm, and a best sensitivity of 45 $\mu$T/$\sqrt{\rm Hz}$ per ($5\,\mu$m)$^2$ pixel. Our portable magnetic imaging instrument may find use in situations where taking the sample to be measured to a specialist lab is impractical or undesirable.