Saturation effects in degenerate four-wave mixing in ruby and GdAIO_3:Cr^+3

In Cr+3-doped crystals the saturation of the excited-state population implies the saturation of the complex nonlinear index of refraction n2, so n2 ∝ (1 + I/Is)−1. We developed a new theoretical model to calculate the efficiency of the degenerate four-wave mixing (DFWM) process in such a saturable nonlinear medium. Our experimental results in ruby and GdAlO3:Cr+3 are in good agreement with the calculations of our theoretical model made using our previous interferometric measurements of n2 in these materials. In the GdAlO3:Cr+3 sample we obtained a maximum DFWM efficiency of approximately 10%, which to our knowledge is the highest value achieved in these kinds of material (Cr+3- or Nd+3-doped materials or organic dyes) with a cw laser.