Refractive index and geometrical thickness measurement of thin optical samples by a transmitted Gaussian beam.

We describe a technique for simultaneously measuring the local geometrical thickness and the refractive index of semi-transparent thin plates by means of the diffractive properties of a transmitted Gaussian beam. The technique is based on measuring the semi-width of the transmitted beam and the shift of the Gaussian centroid caused by introducing a tilt on the sample under test. A homodyne technique is devised to accurately characterize the Gaussian beam. Our proposal does not require any prior information of the sample under study. We present analytical support of our technique and we give experimental results.

Refractive index and geometrical thickness measurement of a transparent pellicle in air by Gaussian beam defocusing.

We demonstrate that it is possible to measure the local geometrical thickness and the refractive index of a transparent pellicle in air by combining the diffractive properties of a Gaussian beam with the analytical equations of the light that propagates through a thin layer. We show that our measurement technique is immune to inherent piston-like vibrations present in the pellicle. As our measurements are based on characterizing properly the Gaussian beam in a plane of detection, a homodyne technique for this purpose is devised and described. The feasibility of our proposal is confirmed by measuring local geometrical thicknesses and the refractive index of a commercially available stretch film.