A new nondestructive characterization technique, based on a modified Maker fringe measurement, is reported that allows the complete determination of complex spatial distributions of the nonlinear χ<sup>(2)</sup>(z) coefficient in planar samples. Each sample under test was stacked together with a phase reference quartz plate to retrieve both amplitude and phase of the optical second-harmonic signal. The added phase information permits the precise determination of the location of the optically nonlinear region within the sample. Hemicylindrical lenses are used to obtain greater internal propagation angles, with an important increase in the information about the nonlinearity distribution. The technique is demonstrated for two Infrasil glass plates thermally poled in vacuum under the same temperature, voltage, and duration conditions. Very different distributions were obtained for these samples, one nonlinear layer being buried 4 μm under the anodic surface while the other was not, the latter exhibiting maximum χ<sup>(2)</sup> three times larger than the former. This difference in the χ<sup>(2)</sup>(z) distribution is explained in terms of charge injection during the poling process.
© 2004 Optical Society of America
Vincent Tréanton, Nicolas Godbout, and Suzanne Lacroix, "Nondestructive interferometric determination of χ(2)(z) spatial distribution induced in thermally poled silica glasses," J. Opt. Soc. Am. B 21, 2213-2220 (2004)