Control loops for a Coupled Dark State Magnetometer

The Coupled Dark State Magnetometer (CDSM) is a new type of scalar magnetometer, which is based on two-photon spectroscopy of free alkali atoms. CDSM measurements do not depend on the sensor temperature. Furthermore, it has no dead zones, no moving parts and no excitation coils at the sensor. This paper deals with the control loops which are developed for tracking the magnetic field dependent resonances and for avoiding drifts of the carrier frequency of the laser diode used as excitation light source. It is the first time that a magnetometer of this type is operated in a control loop. The implementation of several functional blocks in a Field Programmable Gate Array (FPGA) is a first step towards miniaturization for a future space application. The magnetic field magnitude is measured by a frequency. Therefore, the Direct Digital Synthesis (DDS) principle is used for accurate signal generation. A noise floor measurement has shown no 1/f dependence near DC and 70 pT/√Hz up to the corner frequency of 3 Hz for which the CDSM is designed.