Integrating-sphere system and method for absolute measurement of transmittance, reflectance, and absorptance of specular samples

An integrating-sphere system has been designed and constructed for multiple optical properties measurement in the IR spectral range. In particular, fo r specular samples, the absolute transmittance and reflectance can be measu red directly with high accuracy and the absorptance can be obtained from th ese by simple calculation. These properties are measured with a Fourier tra nsform spectrophotometer for several samples of both opaque and transmittin g materials. The expanded uncertainties of the measurements are shown to be less than 0.003 (absolute) over most of the detector-limited working spect ral range of 2 to 18 mum The sphere is manipulated by means of two rotation stages that enable the ports on the sphere to be rearranged in any orienta tion relative to the input beam. Although the sphere system is used for inf rared spectral measurements, the measurement method, design principles, and features are generally applicable to other wavelengths as well. (C) 2001 O ptical Society of America.