We report the design and performance of a non-magnetic drift stable optically
pumped cesium magnetometer with a measured sensitivity of 35 fT at 200 s
integration time and stability below 50 fT between 70 s and 600 s. To our
knowledge this is the most stable magnetic field measurement to date. The
sensor is based on the nonlinear magneto-optical rotation effect: in a
Bell-Bloom configuration a higher order polarization moment (alignment) of Cs
atoms is created with a pump laser beam in an anti-relaxation coated Pyrex cell
under vacuum, filled with Cs vapor at room temperature. The polarization plane
of light passing through the cell is modulated due the precession of the atoms
in an external magnetic field of 2.1 muT, used to optically determine the
Larmor precession frequency. Operation is based on a sequence of optical
pumping and observation of freely precessing spins at a repetition rate of 8
Hz. This free precession decay readout scheme separates optical pumping and
probing and thus ensures a systematically highly clean measurement. Due to the
residual offset of the sensor of < 15 pT together with the cross-talk free
operation of adjacent sensors, this device is uniquely suitable for a variety
of experiments in low-energy particle physics with extreme precision, here as
highly stable and systematically clean reference probe in search for
time-reversal symmetry violating electric dipole moments.Comment: Submitted in AIP Applied Physics Lette