The use of six-wave mixing in a four-level electromagnetically induced transparency (EIT) system with slow probe light was analyzed. It was found that EIT suppressed the linear susceptibility and enhanced the nonlinear susceptibilities in a four-level atomic system. The six-wave mixing at low light intensities was observed due to the suppression of linear susceptibility. The light emission in higher-order nonlinear optical process was viewed due to the diffraction of slow-light off a pure resonant nonlinear grating induced in the four-level EIT medium.
