<title>Surface inspection by optical triangulation</title>

Abstract

We describe an optical noncontact microtopographer based on an active, discrete triangulation procedure, showing that this kind of triangulation based surface inspection system can be applied not only to large distance range sensing but also to smaller samples or smoother surfaces with resolutions that can be driven down to the sub-micron range. In our system the topographic information is obtained from the horizontal shift incurred by the bright spot created by an oblique collimated light beam on a surface when it is displaced vertically. A laser beam is focused onto a small diffraction limited spot on the surface and is made to scan it over the desired region. The horizontal position of the bright spot is perpendicularly imaged onto a linescan camera and the information about the individual detectors that are activated, above a certain controllable intensity threshold level, is used to compute the corresponding horizontal spot's shift on the reference plane. Thus we can compute the distance between the surface and a reference plane at each sampled point. A map of the surface topography can then be built and statistical surface characterization parameters may be calculated. Our laboratory setup's configuration is quite versatile and it has been used for different inspection tasks like: thickness measures and relief mapping of polyethylene films and thin sputtered copper, tin dioxide and silver films, several kinds of fabrics; and roughness measure and topographic inspection of polyethylene molds and graphite samples. Also presented are the portable version of our system and the setup for large distance dimensional assessment.