Bulk second-order nonlinearity was generated in BK7 glass at a higher temperature and with a longer poling time than near-surface second-order nonlinearity. The temporal decay of the bulk second-order nonlinearity was slower than that of the near-surface second-order nonlinearity. The thickness of the near-surface nonlinear layer increased with poling time. Poled BK7 glass was also measured by x-ray photoelectron spectroscopy. Depletion of Na at the anodic surface and its accumulation at the cathodic surface was observed. At the cathodic surface, a higher-energy peak near O (1<i>s</i>) appeared, which shows peroxy-radical defects. At the anodic surface, a lower-energy peak near Si (2<i>p</i>) appeared, which may be attributed to E<sup>′</sup> centers or to two-coordinated Si defects. The mechanisms of generation of these defects and of the second-order nonlinearities are discussed.
© 2002 Optical Society of America
(160.2750) Materials : Glass and other amorphous materials
(160.4330) Materials : Nonlinear optical materials
(190.4160) Nonlinear optics : Multiharmonic generation
(190.4350) Nonlinear optics : Nonlinear optics at surfaces
(240.4350) Optics at surfaces : Nonlinear optics at surfaces
Mingxin Qiu, Toru Mizunami, Ramon Vilaseca, Francesc Pi, and Gaspar Orriols, "Bulk and near-surface second-order nonlinearities generated in a BK7 soft glass by thermal poling," J. Opt. Soc. Am. B 19, 37-42 (2002)