Optimizing longitudinal spin relaxation in miniaturized optically pumped magnetometers

The microfabrication of cesium vapor cells for optically pumped magnetometry relies on optimization of buffer gas pressure in order to maximize atomic coherence time and sensitivity to external magnetic signals. We demonstrate post-bond nitrogen buffer gas pressure tuning through localized heating of an integrated micropill dispenser. We characterize the variation in the intrinsic longitudinal relaxation rate, gamma 10, and magnetic sensitivity, as a function of the resulting nitrogen buffer gas pressure. Measurements are conducted by employing an optically pumped magnetometer operating in a free-induction-decay configuration. gamma 10 is extracted across a range of nitrogen pressures between 60 and 700 torr, measuring a minimum of 140 Hz at 115 torr. In addition, we achieve sensitivities as low as 130 fT/root Hz at a bias field amplitude of about 50 mu T. With the optimal nitrogen buffer gas pressure now quantified and achievable post-fabrication, these mass-producible cells can be tailored to suit a variety of sensing applications, ensuring peak magnetometer performance.