Andreas Pollinger

Enable the inherent omni-directionality of an absolute coupled dark state magnetometer for e.g. scientific space applications

The Coupled Dark State Magnetometer (CDSM) is an optically-pumped absolute scalar magnetometer which is based on two-photon spectroscopy of free alkali atoms. Several magnetic field dependent resonances occur in the presence of an external magnetic field, reaching their maximal strengths at different angles between the magnetic field direction and the reference axis of the sensor defined by the optical path of the laser excitation field. Dependent on this angle the strongest available resonances are selected. This enables an omni-directional dead zone free measurement. The paper discusses the measurement principle, describes the technical realization of the resonance switching, investigates the influence of this transition on the magnetic field measurement and proposes a method to detect the angle of the magnetic field direction in relation to the optical axis. The results presented within this paper show that dead zone free magnetic field measurements are possible with the CDSM without the need of a complex sensor design, e.g. additional moving parts or excitation coils.

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 70pT/√Hz up to the corner frequency of 3Hz for which the CDSM is designed.