Abstract

When a transparent flat plate with parallel surfaces is illuminated with laser-based interferometer, the resulting interference pattern is a complex mixture of fringes created by reflections from both the front and back surfaces of the plate.^1,2 Figure 1 is an example of an interferogram for an optical wedge with perfectly flat surfaces. In order to do meaningful metrology on such an object, the common practice is to either thinly coat the front surface with a high reflectivity material, or defeat the back-surface reflection by applying some kind of index-matching coating. It would be desirable to dispense with these kinds of surface treatments for regular inspection and testing, particularly for process control in a production environment.

© 1994 Optical Society of America