Ion beam enhanced chemical etching of Nd:YAG for optical waveguides

Optical waveguides and waveguide lasers have optical losses and laser gain which are strongly influenced by the preparation of the surface, for example by surface scratches, stress and dislocations generated during polishing. This paper assesses the problems and the depth over which polishing damage is significant for Nd: YAG crystals. The polishing induces a dislocation density in the outer micron of the crystal which exceeds that of high grade laser crystals by similar to 10(6). Removal of the damage layer has been aided by thermal annealing, and almost totally achieved by using ion beam amorphisation of the surface to provide a chemically reactive layer which can be rapidly etched, some 300 times faster than bulk material. The resultant new surface has a surface flatness which is comparable to, or better than the original optical surface. The method of ion beam amorphisation and chemical etching to improve surface quality should be widely applicable, as many crystals can be amorphised by ion beam damage.