Orientational dependence of optically detected magnetic resonance signals in laser-driven atomic magnetometers

resonance (ODMR) have the longest history in the field of atomic magnetometry, and the so-called Mx-magnetometer using a single light beam has proven to be a highly sensitive and robust device. The theoretical modeling of the signals generated by ODMR-based magnetometers is addressed in great detail in a recently published textbook (Chapter 13 in Ref. [3]). ODMR magnetometers infer the modulus B0=ω0/γF of the magnetic field vector B0 from the (driven) Larmor precession frequency ω0 of an atomic vapor’s magnetization, where γF is the gyromagnetic ratio of the used atom (γF/2π ≈ 3.5Hz/nT for Cs). The precession is driven by a much weaker additionally applied oscillating field B1(t) , called the ‘rf-field’. In the standard Mx-magnetometer, a single circularly polarized light beam whose frequency is resonant with an atomic transition is used both to create the medium’s spin polarization by optical pumping [4] and to read out the spin precession signal. The magnetometric sensitivity of an OM, i.e., the smallest magnetic field change that the device can detect (in a given bandwidth), depends on many parameters, such as the light intensity, the atomic number density, the size of the atomic sample, the spin coherence time, and the amplitude of the rf-field. Moreover, the sensitivity critically depends on the relative orientations of the light propagation direction k̂, the rf-field B̂1, and the field of interest B̂0 . The latter dependencies imply that there are, on the one hand, orientation(s) that optimize the device’s sensitivity, and, on the other hand, orientations (so-called dead-zones) for which the sensitivity vanishes. The quantitative understanding of these dependencies is crucial when designing a magnetometer, be it for a laboratory application in which the orientation B̂0 of B0 is mostly known a priori, or for field applications where the knowledge of the dead-zones is of great importance. Abstract We have investigated the dependence of lock-indemodulated Mx-magnetometer signals on the orientation of the static magnetic field B0 of interest. Magnetic resonance spectra for 2400 discrete orientations of B0 covering a 4π solid angle have been recorded by a PC-controlled steering and data acquisition system. Off-line fits by previously derived lineshape functions allow us to extract the relevant resonance parameters (shape, amplitude, width, and phase) and to represent their dependence on the orientation of B0 with respect to the laser beam propagation direction. We have performed this study for two distinct Mx -magnetometer configurations, in which the rf-field is either parallel or perpendicular to the light propagation direction. The results confirm well the algebraic theoretical model functions. We suggest that small discrepancies are related to hitherto uninvestigated atomic alignment contributions.