Enhanced Kerr nonlinear effect of Raman transition in a A-type three-level atomic system

We report a theoretical study of linear and nonlinear susceptibilities of Raman transition in a A-type three-level atomic system. In the Raman transition, if the population of atoms is all prepared in the ground state which interacts with the control light, the linear susceptibility equals zero, while the third-order nonlinear susceptibility does not equal zero. By decreasing the nonradiative decay rate γ between the two ground states of the atoms, the Kerr nonlinear refractive index for cross-phase modulation can be significantly enhanced.