A focusing reflectometer for measuring the optical constants of thin films by the (Rø) method is described. The focusing reflectometer has a larger effective aperture than typical planar reflectometers, and, unlike planar reflectometers, the illuminated area of the specimen is independent of the angle of incidence. The intensity of the incident light is not measured so the reflectometer is limited to wavelengths where the reflectivity of the specimen varies rapidly with the angle of incidence. Results are given for evaporated gold films in the energy range 6.0 eV to 12.0 eV.
R. E. Burge, A. T. Davidson, J. C. Draper, G. R. Field, and E. Murphy, "New Focusing Reflectometer for Measuring Optical Constants of Thin Films," Appl. Opt. 10, 342-345 (1971)