Multiple-pass reflectometer

Abstract
The multiple-pass reflectometer has been shown to be a convenient and precise instrument for measuring absolute spectral reflectance values in excess of 0.99. Given here is an extension of earlier work. We present details of the setup, operation, parameter optimization, and some limitations of the reflectometer. For a carefully aligned instrument the precision of the measurement is limited by the uncertainty in the computer fit of a straight line to the data. For the UV and visible spectral regions, typical reflectance precision is a few parts in 104. Systematic errors due to nonuniform photosurfaces and astigmatism have been minimized for the setup described here.