The self-Kerr-nonlinearity of a four-level $\mathsf{N}$-type atomic system is studied both experimentally and theoretically. The self-Kerr-nonlinear coefficient $n_2$ of the probe beam is greatly enhanced near atomic resonance, and can be dramatically modified by changing the switching laser power. With an increasing switching laser power, the slope of the Kerr nonlinear coefficient $n_2$ around the atomic resonance changes from negative to positive, and the value of $n_2$ varies from ∼–4 × 10${}^{-6}$ to 4 × 10${}^{-6}$ cm${}^2$/W at certain near-resonant probe frequency detunings. Such controllable Kerr nonlinearity can find applications in optoelectronic devices, such as all-optical switching and logic gates.

• Received 31 August 2011

DOI:https://doi.org/10.1103/PhysRevA.84.053820