Pump-probe nonlinear magneto-optical rotation with frequency modulated   light
  Specific types of atomic coherences between Zeeman sublevels can be generated and detected using a method based on nonlinear magneto-optical rotation with frequency modulated light. Linearly polarized, frequency modulated light is employed to selectively generate ground-state coherences between Zeeman sublevels for which $\Delta m=2$ and $\Delta m=4$ in $^{85}$Rb and $^{87}$Rb atoms, and additionally $\Delta m=6$ in $^{85}$Rb. The atomic coherences are detected with a separate, unmodulated probe light beam. Separation of the pump and probe beams enables independent investigation of the processes of creation and detection of the atomic coherences. With the present technique the transfer of the Zeeman coherences, including high-order coherences, from excited to ground state by spontaneous emission has been observed. 
S. Pustelny, D. F. Kimball, S. M. Rochester, V. V. Yashchuk, W.   Gawlik, D. Budker