Simultaneous measurement of refractive index and thickness of transparent material by dual-beam confocal microscopy

We propose and demonstrate a novel technique, termed dual-beam confocal microscopy, for the simultaneous measurement of the refractive index and geometrical thickness of a single layer. The technique is based on the creation of two closely spaced lateral confocal gates for the two orthogonal polarization states of a laser beam in a sample via a Nomarski prism. Thereafter, by applying Gaussian beam theory, the refractive index can be determined with an error of 1% or less for a commercial cover glass. Based on the measured refractive index, the thickness of the sample can also be calculated. To verify the proposed methodology and optical setup, a microlens array was scanned, with the surface profile and refractive index subsequently compared with their catalog specifications.