Enhancing detection of low-coherence interferometry signals acquired with a spatial heterodyne detector

Abstract

The use of low-coherence interferometry for industrial applications is constantly growing due to its non-destructive nature and high resolution. Fourier domain systems are usually preferred as they provide a scanning-free method. Recently, a spatial heterodyne detector has proved to be useful in extending the measuring range without losing the micrometric resolution. This system Fourier transforms the interferometric signal, giving the information of interest as fringes in the output image. However, for low light intensities, the images might need to be processed to facilitate the visualization and detection of these fringes. In this work we analyze two main approaches to achieve this: one that uses a cross correlation method and the other one that uses a specially designed two-dimensional adaptive filtering technique. Both methods showed an improved performance when compared with conventional image processing techniques, enhancing the fringes contrast. Additionally, we showed that combining normalized cross correlation and the image gradient is an effective method to locate low intensity signals.