Preparation of ultralow loss mirrors with reflectivity of over 99.9968%

Ultralow loss mirrors (at the wavelength of 1315 nm) were prepared by RF ion beam sputtering with materials of tantalum oxide and silicon oxide. The mirror loss (A + S + T), including directly measured transmission, scattering, and absorption, respectively, is less than 32 ppm, which corresponds to a reflectivity of over 99.9968%. This is the highest reflectivity achieved at this wavelength in published reports.