Magnetic fields play an important role in many plasma environments, from fusion to space plasmas to magnetic reconnection. Quantum beat spectroscopy is a non-perturbative laser-based optical diagnostic that has demonstrated near-single shot, sub-Gauss precision measurement of the magnetic field strength in argon and helium plasmas, with sub-millimeter spatial resolution and temporal resolution on the order of 101-102 ns. In this work, the measurement technique is expanded to include the magnetic field orientation and, in a specific case, the absolute direction. The measurements of the quantum beat amplitudes are made at three separate polarization angles to determine their phase shift. The vector components of the magnetic field are then analytically determined as a function of the measured phase shift of the quantum beat amplitudes. The validity of this technique is demonstrated through a correlation between a set of known magnetic field angles and the measured phase shift for each angle, with a standard deviation of 5.7° and reduced χ2 result of 0.94. The estimated uncertainty in the calculated magnetic field components is less than 10%.
Gilbert et al. (2026) studied this question.