Splitting of an electromagnetically induced transparency window of rubidium atoms in a static magnetic field

We study the phenomenon of electromagnetically induced transparency (EIT) of Rb-87 vapor at the temperature of 325 K in a magnetic field. Two linearly polarized orthogonal laser fields act on two dipole-allowed transitions of the D1 line of Rb-87 in the Lambda configuration, respectively. In the absence of magnetic fields, we observe a wide EIT window with the contrast of about 66% while when the magnetic field is applied, the wide EIT window is split into three or four narrower subwindows with contrasts of 32% or 16% due to the lifting of magnetic sublevels' degeneracy. The number of EIT subwindows depends on the magnetic field orientation. Our theoretical simulations and analysis are in good agreement with the experimental results.