M.Sc Thesis

M.Sc StudentDikopoltsev Mark
SubjectA Study of the Spin Exchange Relaxation-Free Regime
in Magnetometry
DepartmentDepartment of Physics
Supervisors PROF. Jeff Steinhauer
DR. Moshe Schuker


Alkali-metal magnetometers measure magnetic fields using the coherent precession of polarized atomic spins, where the spin exchange decoherence process is typically the main limiting factor. The spin exchange relaxation-free (SERF) magnetometer completely eliminates decoherence due to spin exchange collisions by operating with high density atomic vapor in very small magnetic fields. SERF implementation has made the alkali magnetometry overcome the SQUID magnetometers, and as of today the alkali magnetometers have the highest fundamental sensitivity. SERF magnetometers can be used in a variety of applications such as brain activity sensing in medicine or precise angular measurements in navigation.

In this thesis we describe a research on several aspects of the SERF regime in alkali magnetometry. We examine two main features of the SERF regime: the restriction to low magnetic fields and the high atomic density of the atomic vapor. On the subject of low magnetic fields we study the common resonant methods for magnetometry and it’s limit and place restrictions on its operation. For example, we use Floquet theory approach to show that the deviation from the rotating wave approximation increases with the magnitude of the resonant field and that for small enough RF magnetic fields the rotating wave approximation extends over the "traditional" limits. On the subject of high density we study the probing and excitation of dense atomic vapor and analyze a new scheme for the differential magnetic probing in high density alkali that uses Bessel beam geometry. We also demonstrate experimentally nonlinear effects of the birefringent coherence in the SERF regime as a result of the high density and high collision rate, and show that high magnetic moments of the atoms also go through SERF. Moreover, the transition to SERF occurs when the magnetic field is below the Larmor frequency and not as one would expect in twice the Larmor frequency.