Enhanced second harmonic generation at surface in transparent nanocrystalline TeO2-based glass ceramics

Transparent TeO2-based glass ceramics consisting of nanocrystalline particles such as 15K(2)O.15Nb(2)O(5).70TeO(2) have been prepared, and the effect of surface layers on the second harmonic (SH) intensity has been examined using the Maker fringe method. An enhanced second harmonic generation (SHG) with fine fringe patterns has been observed at the original surface layers in transparent glass ceramics. The thickness of the surface layers giving a strong SHG is estimated to be around 50 mu m, which is much larger than the coherence length of 3.5 mu m for the glass ceramics. The glass ceramics without the original surface layers obtained by mechanical polishing show weak SH intensity, and any fringe pattern is not observed. Any evidence for an orientation of crystals at the surface has not been confirmed, and the origin of an enhanced SHG is unclear at this moment. (C) 2000 American Institute of Physics. [S0003- 6951(00)00140-6].