Our study of highly reflective (HR) dielectric coatings prepared by the sol-gel process has indicated that hydrated alumina and silica are the materials of choice for the high and low index components respectively.

We can now prepare 32–36 quarter-wave-layer samples from colloidal suspensions of the relevant oxides by spin coating at room temperature. These have reflectivities of about 99% and damage thresholds in the range 30–40 J/cm² at 1064 nm with 16 ns pulses at 30 Hz. This threefold improvement in threshold over that reported earlier for this system was attributed to an improvement in the preparative technique particularly in regard to cleanliness. Coatings have been prepared recently on substrates up to 8” in diameter and scale-up development continues.