Intensity dependence of optically encoded second-harmonic generation in germanosilicate glass: Evidence for a light-induced delocalization transition

Experiments on the ir intensity dependence of the preparation process for second-harmonic generation in germanosilicate fibers and preforms reveal that a sharp threshold of the order of 5 GW/${\mathrm{cm}}^2$ exists. The results are explained in terms of a charge-delocalization transition that occurs due to the renormalization of the disorder energy between localized states dressed by an intense nonresonant light field.