Abstract
Two Beam Interferometers, Multiple Beam and Multipass Interferometers are frequently used for the detection and the visual measurement of thickness, phase or refractive index weak variations. These variations are revealed by an interference fringe shift.
A quantitative study of the perceptible limit shift allows to define and study the interferometer sensibility and to compare the different interferometers.
The Multipass Interferometry appears to be the most sensitive technic for the very weak thickness variation measurements (below 200 Å); this result implies an important number of passes (higher than twenty) to be possible.