Third-order optical nonlinearity induced by effective mass gradient in heterostructures

In semiconductor heterostructures the electron effective mass can vary spatially, giving rise to a nonlinear force parallel to the mass gradient. In an optical field this nonlinear force modulates the electron mass through its position dependence, leading to a novel third order optical nonlinearity. The susceptibility of this process is calculated through the kinetic equations for the electrons. It is found that large nonlinear refractive indices can be obtained with subpicosecond relaxation times. Possible device configurations are discussed.