EVALUATION OF CORRECTION FACTORS FOR TRANSMITTANCE MEASUREMENTS IN SINGLE-BEAM INTEGRATING SPHERES

An integrating sphere for transmittance measurements at normal and obl ique angles of incidence has been constructed. The sphere is a single- beam instrument that uses a small-area silicon diode as the detector. The entry port is only 0.37% of the total wall area and has an oblong shape to permit measurements at high angles of incidence for scatterin g samples. A small beam size has been made possible by using a low-noi se preamplifier system for the detector circuit. The oblong port shape and a small beam size make it possible to perform simulated double-be am measurements at near-normal incidence. Modified correction factors for the sample reflectance have been derived. Special attention has be en paid to the separation into a diffuse and a specular component of t he transmitted light. Results have been compared with the results of m easurements on a double-beam instrument, and the correction factors fo r specular and diffuse samples have been experimentally verified. The importance of using the right correction factors for different types o f samples has been evaluated together with the influence of the sphere parameters.