Interpretation of integrating sphere signal output for non-Lambertian samples

A new formalism is derived for the analysis of signal output from double-beam integrating spheres. The analysis explicitly considers the effects of port losses and a non-Lambertian sample surface and introduces a separation of the diffusely reflected light into two parts: one which should be analyzed as a specular component and one which is fully diffuse. An experimental procedure to determine the two parameters in the formalism is described for two cases, a brushed copper and a rolled aluminum surface, and it is experimentally verified that the formalism eliminates spurious structure from the barium sulfate reference. A criterion is also given for the selection of barium sulfate or polytetrafluorethylene powder as a reference material.