Polarization-independent reflectance matching (PRIM): A technique for the determination of the refractive index and thickness of transparent films

The reflectances of the coated and uncoated areas of a substrate which is partially covered by a transparent film of uniform thickness are matched, for any state of polarization of the incident light, at a set of discrete angles of incidence whose number depends on film thickness. Detection of such angles of incidence for PIRM provides a very simple and accurate technique for the simultaneous measurement of thickness and refractive index of transparent thin films on any substrate. The necessary equations for applying this technique are given and a study is made of the effect of film thickness and refractive index on the availability and number of angles of incidence for PIRM.