Instruments for making precision measurements of the specular reflectance at essentially normal incidence in the near ultraviolet, visible, and infrared regions of the spectrum are described. The square of the absolute reflectance is measured, with a resultant increase in measuring precision, and the major sources of systematic error in making reflectance measurements have been reduced or eliminated. The difficulty in making precision reflectance measurements in the infrared, where integrating spheres cannot be used, has been overcome by a unique compensating feature in the infrared reflectometer which prevents the image on the detector from changing size or position because of a slight tilt of the sample. The measurements made with these instruments on high reflectance samples are believed to be good to ±0.001.
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