Simultaneous measurement of thickness and refractive index by a single-channel self-mixing interferometer

The authors introduce a new method for the simultaneous measurement of thickness d and refractive index n of transparent slabs and thin films. The method is based on the optical phase shift measured by a single-channel, self-mixing interferometer (SMI) as a function of the angle of incidence on the sample. The authors use a motorised rotating stage to apply an angular scan up to ±65° to the sample. Then, the authors analyse the derivative of phase difference with respect to the rotation angle, apply a standardisation and fit it to the theoretical expression and after a few iterations they are able to simultaneously determine n and d, with a typical accuracy of 0.02 and 1%, respectively.