Chopped nonlinear magneto-optic rotation: A technique for precision measurements

Department of Physics, Indian Institute of Science - Bangalore 560 012, India

^a vasant@physics.iisc.ernet.in

Received: 7 March 2011
Accepted: 19 April 2011

Abstract

We have developed a technique for precise measurement of small magnetic fields using nonlinear magneto-optic rotation (NMOR). The technique relies on the resonant laser beam being chopped. During the on time, the atoms are optically pumped into an aligned ground state (Δm=2 coherence). During the off time, they freely precess around the magnetic field at the Larmor frequency. If the on-off modulation frequency matches (twice) the Larmor precession frequency, the rotation is resonantly enhanced in every cycle, thereby making the process like a repeated Ramsey measurement of the Larmor frequency. We study chopped-NMOR in a paraffin-coated Cs vapor cell. The out-of-phase demodulated rotation shows a Lorentzian peak of linewidth 85 μG, corresponding to a sensitivity of . We discuss the potential of this technique for the measurement of an atomic electric-dipole moment.