Dimensional characterization of large opaque samples and microdeformations by low coherence interferometry

Abstract

We report on the application of an interferometric system based on the low-coherence interferometry technique to the dimensional characterization of large opaque mechanical parts as well as microdeformations experienced by them. The implemented scheme is capable of simultaneously measuring very small deformations and relatively large dimensions or thicknesses (several centimeters) of the sample. By applying the chirp Fourier transform algorithm, it was possible to measure changes in thickness with an uncertainty of 0.35 μm when a 7-cm-thick sample was measured. The measurement scheme was implemented in optical fiber, which makes it highly adaptable to industrial conditions. It employs a tunable light source and a Sagnac-Michelson configuration of the interferometric system that allows the thickness of the opaque sample and the topography of both faces to be obtained simultaneously. The developed system can be used to perform profilometry of opaque samples and to analyze the dimensional behavior of mechanical pieces in production lines or under mechanical efforts capable of introducing some deformations on them. This feature enables the system to perform quality control in manufacturing processes.