METHOD AND APPARATUS FOR AUTOMATIC OPTICAL INSPECTION

An inspection system for providing high contrast images of two materials of an article to be inspected is disclosed. Light with variable spectral range and large angular coverage is passed from the source through a polarizer, reflects from or is transmitted through the article to be inspected, passes through an analyzer and is detected by a sensor. A phase compensator is disposed either between the polarizer and the sample or the sample and the analyzer. Two of the three polarization optical components, that is, the polarizer, the compensator and the analyzer, are separately adjusted until the maximum contrast is found in the image. This enables high contrast imaging of surfaces of objects of similar optical reflectivity, (such as surfaces consisting of two similar specular materials, or surfaces partly covered with transparent films) which cannot be imaged using normal reflective image forming techniques. The system of the invention can also be operated to measure the thickness or index of refraction of transparent thin films.