Detection of surface cracks, pits, and scratches in highly reflective and low-emissive materials by using a laser beam trapping and infrared imaging technique

The purpose of this paper is to describe an infrared inspection system for highly reflective and low emissive materials. The detection system was developed for identifying surface irregularities such as cracks, pits, scratches and holes in part that are made of materials having high reflectivity and a low emissivity, such as polished titanium, aluminum, a silicon panels. In this technique, a laser beam is focused to a diameter that is approximately 50 microns or less that scans across the surface of the part under inspection. Energy from the beam is trapped inside a crack or pit, which results in a significant thermal gradient increase. This high thermal gradient will overcome the reflection from the surroundings and can be detected by an infrared imager.