Two-wave mixing by phase and absorption gratings in saturable absorbers

Two-wave mixing (TWM) by means of moving phase and absorption gratings is reported for acridine-doped glass and ruby. A measurement method is described that enables TWM from the phase and absorption gratings to be determined independently, leading to a value for the ratio of the real part of the nonlinear index n2 to the imaginary part that is independent of beam intensity profiles or overlap conditions. An anomalous TWM response was observed from the absorption grating in ruby.