The integrating sphere is manipulated by means of two rotation stages that enable the ports on the sphere to be rearranged in any orientation relative to the input beam

An integrating sphere system has been designed and constructed for multiple optical properties measurement in the IR spectral range. In particular, for secular samples, the absolute transmittance and repentance can be measured directly with high accuracy and the absorptions can be obtained from these by simple calculation. Although the sphere system is used for infrared spectral measurements, the measurement method, design principles, and features are generally applicable to other wavelengths as well. The sphere is manipulated by means of two rotation stages that enable the ports on the sphere to be rearranged in any orientation relative to the input beam. The expanded uncertainties of the measurements are shown to be less than 0.003 ~absolute! over most of the detector-limited working spectral range of 2 to 18 mm. These properties are measured with a Fourier transform spectrophotometer for several samples of both opaque and transmitting materials.

An important application of integrating spheres is their use as an averaging device for detectors. Because of the useful properties of the sphere, an averaging sphere’s entrance port can be both significantly larger and much more spatially uniform than a bare detector. The beneath of using the integrating sphere for more accurate detection of light are used in the design of the system and development of the method presented in this paper. The trade-off made for these improvements is a degradation of the signal-to-noise ratio. The inherent problems of sphere spatial no uniformity are overcome through judicious use of the symmetries of the sphere design to establish symmetries in the measurement geometry. The measurement of absolute transmittance (t), repentance (r), and absorptions (a) of secular samples is described and demonstrated.

After describing the spastics of the integrating sphere in Section 2, the other components of the sphere system in Section 3, and the absolute measurement method in Section 4, we present the sphere characterization measurement results for error analysis in Section 5. The achievement of measurement uncertainties of 0.002 to 0.004 are demonstrated in Section 6 for several common IR materials. Finally, Section 7 contains the discussion of the results with conclusions about the usefulness of the sphere method for secular materials.