The use of digital signal processing techniques for the interferometric profiling of rough surfaces

Abstract

Conventional non-contact optical methods of surface profiling are limited in the range of surface heights that can be accurately measured due to phase ambiguity errors on steep local slopes. Instruments that have been developed thus far to avoid the problems with local slope typically suffer from poor measurement height resolution and slow measurement speeds. Contact profilometers such as stylus-based instruments suffer from poor lateral resolution due to the finite radius of the stylus tip, and slow measurement speeds, especially when two-dimensional scans of the surface are required. Stylus tips can also scratch delicate surfaces during the measurement. We propose a new method of optical, non-contact profiling of rough surfaces without the limitations on local slope that other methods suffer from. This new method utilizes interferometric techniques as well as digital signal processing algorithms to produce fast, accurate, and repeatable three-dimensional surface profile measurements on a wide variety of surfaces.