INCOHERENT REFLECTION PROCESSES - A DISCRETE APPROACH

A formalism for calculating the reflectance and transmittance of optic al media consisting of discrete elements is described, in the case whe re the reflected and transmitted beams from each element are incoheren tly related to those from the other elements. The elements may be abso rbing and may have unequal reflectances from each side, The formalism of Kubelka and Munk [P. Kubelka and F. Munk, Z. Technichse Physik 12 ( 1931) 593] originally developed for scattering media, is shown to give equivalent results. The discrete formalism is applied to media consis ting of stacked slides, and to combinations of interference filters. T he filter example has particular relevance to the problem of eye sight protection against lasers. Results indicate that the high reflectance associated with many narrow band filters can lead to a substantial in crease in transmission when more than one filter is used in combinatio n. Experimental measurements are used to illustrate and verify the the ory.