Nonlinear magneto-optical rotation - A possible tool for sensitive magnetometry

Optical pumping in an alkali metal vapour produces long-standing coherences of ground state Zeeman sub-levels. These coherences produce large nonlinear magneto-optic rotation (NMOR). Techniques using optical coherences for sensitive magnetometry have been in vogue for a long time. However, the sensitivity achieved has been three orders of magnitude lower than that of a SQUID magnetometer. The NMOR technique has yielded signals having a very narrow width of a few micro-Gauss. In principle, it has been demonstrated that with NMOR magnetometers one can obtain a sensitivity matching, or better than the sensitivity of a Squid magnetometer. There are still many problems to be resolved before these magnetometers can be put to use in geomagnetic and biological applications, where small magnetic fields need to be measured.