METHOD OF AND APPARATUS FOR MEASURING THE THICKNESS AND THE REFRACTIVE INDEX OF TRANSPARENT MATERIALS

摘要

The invention is based on phase difference measurements. A Zeeman effect laser (3) generates a light beam (4) containing two radiations with slightly different frequencies whose beat is generated at the end of a path external to the material (1, 2a, 101). The same beam is split into the two component radiations (4c, 4d); the beats are generated between the first radiation, which is made to follow a path outside the material, and two radiations obtained by making the second radiation follow two different paths inside the material. The phase differences of these two beats with respect to the first are measured by a phase-comparison system (20, 21), and the refractive-index values as well as the thickness values are obtained by suitable computing means.