Double fitting of Maker fringes to characterize near-surface and bulk second-order nonlinearities in poled silica

An experimental analysis of the distribution and thickness of the bulk nonl inearity induced in poled silica is reported. The second-order susceptibili ty decreases exponentially from the anodic interface. Maker fringe patterns showing a double structure are interpreted in relation to the presence of two nonlinear profiles. one concentrated near the anodic surface and anothe r extending into the bulk of the sample. The Maker fringe theory is properl y generalized and a double fitting technique reproducing well the experimen tal results is used to characterize the induced nonlinearities. The depende nce of the second-harmonic signal on the poling temperature is given, which is different from that of sol-gel silica. (C) 2000 American Institute of P hysics. [S9003-6951(00)02923-5].