Nonlinear magneto-optical rotation with frequency-modulated light in the geophysical field range

Recent work investigating resonant nonlinear magneto-opticalrotation (NMOR) related to long-lived (tau_rel approx 1s) ground-stateatomic coherences has demonstrated potential magnetometric sensitivitiesexceeding (10-11 G Hz-1/2) for small (<1 micro G) magnetic fields. Inthe present work, NMOR using frequency-modulated light (FM NMOR) isstudied in the regime where the longitudinal magnetic field is in thegeophysical range (sim 500mG), of particular interest for manyapplications. In this regime a splitting of the FM NMOR resonancedue tothe nonlinear Zeeman effect is observed. At sufficiently high lightintensities, there is also a splitting of the FM NMOR resonances due toac Stark shifts induced by the optical field, as well as evidence ofalignment-to-orientation conversion type processes. The consequences ofthese effects for FM-NMOR-based atomic magnetometry in the geophysicalfield range are considered.