Optimum parameters to etch Nd:YAG crystals with orthophosphoric acid H3PO4

Subsurface flaws, which determine the fracture strength of crystals, can be removed by the aid of chemical etching. Above a temperature of 200°C orthophosphoric acid H3PO4 is an efficient etchant for yttrium aluminium garnets. However, at these temperatures the etchant decomposes into its related phosphoric acids which show negligible etching rates for garnets. It takes a long time to warm up a large volume of acid and the etchant is decomposed for the most part already before the optimum temperature is reached. We show that efficient etching is achieved when the samples are in the bath already during the warm-up phase and specify the parameters for the optimum etch process.