Coupled dark state magnetometer for the China Seismo-Electromagnetic Satellite

The coupled dark state magnetometer (CDSM) is an optically pumped scalar magnetometer, which is based on two-photon spectroscopy of free alkali atoms. This paper introduces the measurement principle, instrument design, required resources and key performance characteristics of the flight model for the China Seismo-Electromagnetic Satellite, which is the first demonstration of the CDSM measurement principle in space. The CDSM uses several coherent population trapping (CPT) resonances in parallel in order to reduce systematic errors, e.g. the sensor temperature dependence. Overall five control loops were identified to enable a reliable operation. As known so far CPT is the only effect in optical magnetometry which inherently enables omni-directional, dead-zone-free measurements. This leads to a simple all-optical sensor design without double cell units, excitation coils or electromechanical parts. The instrument is characterized by an accuracy of 0.19 nT (σ), a detection noise of 50 pTrms at 1 s integration time, a mass of 1672 g and an in-Earth orbit measured power consumption of 3394 mW. (paper)