Correlation between substrate preparation technique and scatter observed from optical coatings

We present experimental evidence of the dependence of coating scatter on a substrate preparation technique for fused silica substrates. Samples included conventionally polished, superpolished, andfloat-polished substrates. We used scatterometry and total internal reflection microscopy to investigate the effects of substrate preparation on the performance of zirconium oxide thin films. Results indicate that scatter from coatings dominates the scatter signature of the coated optic. They also demonstrate that substrate preparation can affect the level of scatter produced in optical coatings. In addition it is observed that the substrates with the lowest scatter do not necessarily result in the coatings with the lowest scatter.