Versatile high-precision multiple-pass reflectometer.

A confocal mirror assembly is used to measure radiant reflectances in excess of 0.99 with high precision. The mirrors can be either plano or curved with a few diopters of power, and the angle of incidence can vary from 5 degrees to 70 degrees . Multilayer dielectric reflectors consisting of alternate layers of tantalum pentoxide and silica were prepared by evaporation in a vacuum. A maximum reflectance of 0.9996 +/- 0.0002 was measured at 520 nm.