We present the design process and implementation of fully open-source, ultra-low noise programmable current source systems in two configurations. Although originally designed as coil drivers for Optically Pumped Magnetometers (OPMs), the device specifications make them potentially useful in a range of applications. The devices feature a bi-directional current range of ± 10 mA and ± 250 mA respectively on three independent channels with 16-bit resolution. Both devices feature narrow 1/f noise bandwidth of 1 Hz, enabling magnetic field manipulation for highperformance OPMs. They exhibit low noise of 146.3 pA/ √ Hz and 4114 pA/ √ Hz which translates to 14.57 ppb/ √ Hz and 16.46 ppb/ √ Hz noise relative to full scale.

Magnetic field imaging is a valuable resource for signal source localization and characterization. This work reports an optically pumped magnetometer (OPM) based on the free-induction-decay (FID) protocol, that implements microfabricated cesium (Cs) vapor cell technology to visualize the magnetic field distributions resulting from various magnetic sources placed close to the cell. The slow diffusion of Cs atoms in the presence of a nitrogen (N2) buffer gas enables spatially independent measurements to be made within the same vapor cell by translating a 175 µm probe beam over the sensing area. For example, the OPM was used to record temporal and spatial information to reconstruct magnetic field distributions in one and two dimensions. The optimal magnetometer sensitivity was estimated to be 0.43 pT/ √ Hz within a Nyquist limited bandwidth of 500 Hz. Furthermore, the sensor's dynamic range exceeds the Earth's field of approximately 50 µT, which provides a framework for magnetic field imaging in unshielded environments.