Application of a differential optical atomic magnetometer to ultra-low field NMR detection

We report on a dual-channel magnetometer based on non-linear magneto optical rotation in Cs buffered glass cell. The Cs atoms are optically pumped and probed by free running diode lasers tuned to the D₂ line. A wide frequency modulation of the pump laser is used to produce both synchronous Zeeman optical pumping and hyperfine repumping. The magnetometer works in an unshielded environment and spurious signal from far located magnetic sources is rejected by means of differential measurement. The head consists of two cells where probe and a pump beams cross each other at a small angle. The probe beams are analyzed by means of balanced polarimeters.