Detection and removal of surface defects in optical materials

Numerous insulating materials are used as substrates for optical waveguide versions of lasers, second harmonic generation, electro-optics and photonic devices but, independent of the production methods, the losses in the guid es are considerably worse than those of bulk material. It is therefore esse ntial to overcome this major problem, not least because success would allow a much wider range of materials to be included in waveguide applications, (e.g. by developing low gain systems such as tuneable laser waveguides). An obvious source of the loss occurs in the cutting and polishing of the surf ace since, although the outer layer may be optically flat, the subsurface i s highly strained and has a high dislocation density to depths of several m icrons (i.e. precisely in the depth regime where the waveguides are formed) . Such dislocation problems can be revealed and, in the case of Nd:YAG, imp rovements introduced by amorphisation and chemical etching of the surface, to generate a damage free surface layer. Once the damaged YAG layer was rem oved cathodoluminescence (CL) intensity increased by 250%, SHG effects were noted, and for waveguides photoluminescence increased by 40% and transmiss ion was improved. The method employed may be applied much more widely (e.g. in garnets, LiNbO3, Quartz and phosphates).