Resonant nonlinearity enhancement in rubidium vapor with additional optical pumping

We investigate the enhancement of characteristic nonlinear phase shift in warm rubidium vapor for a signal beam using an additional pump laser at different frequency. A numerical model based on density matrix formalism is used. Experimental results of self-rotation and diffraction in a three-wave mixing process as well as beam amplification are shown. For 87Rb transition D2 line with Fg = 1, the nonlinearity to absorption ratio can be enhanced approximately two times with a pump beam tuned at Fg = 2 transition in a co-propagating scheme, which produces strong nonlinear interaction for Fg = 1 line at signal beam powers of ~10 mW.