Growth rate of second-harmonic generation in glass

We study the growth rate of the light-induced second-order nonlinearity in germanium-doped optical fiber preforms. We seed the glass with both infrared light and green light (Nd:YAG and doubled Nd:YAG) to create the second-order nonlinearity and measure its formation rate while varying the intensity of either the fundamental or the second-harmonic seeding beams. We find that the formation rate varies as a power law of the intensities, but with an exponent larger than predicted by recent models.