Coupled dark state magnetometer for the China Seismo-Electromagnetic Satellite

Abstract

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.

Simultaneous Observations of ELF/VLF Rising‐Tone Quasiperiodic Waves and Energetic Electron Precipitations in the High‐Latitude Upper Ionosphere

“…The background geomagnetic field is measured by the high‐precision magnetometer (HPM), which includes two fluxgate sensors (Cheng et al, 2018) and a coupled dark‐state magnetometer (Pollinger et al, 2018), providing both vector and scalar values of the total geomagnetic field at a frequency range from DC to 15 Hz. The variant magnetic field from 10 Hz to 20 kHz is measured by a three‐axis search coil magnetometer (SCM) mounted on the end part of a 4.5 m long boom to avoid the artificial electromagnetic interference induced by satellite platform (Cao et al, 2018).…”

First in-orbit results of the vector magnetic field measurement of the High Precision Magnetometer onboard the China Seismo-Electromagnetic Satellite

“…No moving parts, feedback coils, and active electronics at the sensor are needed for an omnidirectional magnetic field measurement. Furthermore, the CDSM uses three CPT resonances in parallel which reduces systematic errors significantly (Lammegger 2008;Pollinger et al 2018). Figure 5 shows the block diagram of the CDSM flight model, which consists of the mixed signal electronics board and the laser unit which are mounted in the instrument box.…”

“…The sensor unit is connected to the electronics with two fibers and two twisted pair cables. Five control loops are required to track the magnetic field-dependent Zeeman resonances, to track the rubidium D1 fine structure transition with the current and temperature dependent laser carrier frequency, to track the rubidium D1 hyperfine structure transition with the microwave generator, and to heat the sensor unit for temperatures below 18 °C (Pollinger et al 2018).…”

Magnetic field data processing methods of the China Seismo-Electromagnetic Satellite

“…Theoretically, the measurement error caused by Zeeman nonlinear frequency shift of the Rb 87 atom can be eliminated utilizing signal superposition produced by the double CPT effect of the CDSM. However the change of the angle between magnetic field direction and probe laser incidence direction will still produce small measurement errors, which can be accurately determined and corrected by ground calibration (Pollinger et al, ).…”