Use of hafnium dioxide in multilayer dielectric reflectors for the near uv

We measured the refractive index of layers of hafnium dioxide that were prepared by evaporation in a vacuum. It is transparent to wavelengths as short as 230 nm. Its refractive index at 300 nm was as high as 2.10 or as low as 1.90, depending upon the conditions of evaporation. Tests at Los Alamos Scientific Laboratory indicate that its laser damage threshold is approximately 2 J/cm(2) at a wavelength of 355 nm. Multilayer dielectric mirrors were prepared using hafnium dioxide and silicon dioxide. The radiant reflectance exceeded 99% at a wavelength of 320 nm.