Characterization of alkali-metal vapor cells fabricated with an alkali-metal source tablet

Abstract

Optically pumped magnetometers (OPMs) that use alkali metal vapor cells can measure weak magnetic fields generated by the human body. A multichannel detector head with alkali-metal vapor cells mounted in arrays is employed to assure spatial resolution for real-time biomagnetic imaging of various body surfaces. However, further development of alkali metal vapor cell fabrication processes is required to obtain cells with uniform magnetic field sensitivities together with sufficient sensitivity of each individual cell. Herein, the authors propose the fabrication of alkali metal vapor cells for OPM arrays using alkali metal source tablets (AMSTs) as alkali metal dispensers. An AMST is a three-dimensional microstructure that contains precise quantities of the chemical precursors that are used to produce pure alkali metals by low temperature thermal decomposition and to fill reproducible quantities of these metals into cells. In this work, the K production efficiency was characterized with respect to the particular chemical precursors and AMST microstructure employed, and the potential of K-filled glass cells fabricated using AMSTs as components of OPM arrays was demonstrated. An AMST composed of KN3 deposited on porous alumina with 60 μm pore sizes exhibited the most efficient performance during the fabrication of K-filled glass cells. The magnetometric sensitivity obtained with eight K-filled cells was found to be in the range of 3.3–3.8 fTrms/Hz1/2 at a resonance frequency of 10 kHz.