Recently, surface measurement devices utilizing wavefront measuring Phase Shift Interferometry interfaced with a computer system have been introduced and used in industry. These devices provide a non-destructive means by which the surface texture of a precision manufactured product can be measured at a several nanometer accuracy level. However, the biggest problem common on to all forms of Phase Shift Interferometry is unwrapping the phase. Simple phase unwrapping algorithms assume that every pixel is within π radians of its neighbors. If this is true, any reasonable algorithm will return the correct unwrapped phase. If not, correct unwrapped phase will not be obtained. In rough surface, frequently, neighboring pixels have phase steps greater than π. This paper proposes the new method which makes phase steps smaller than π by sub-pixel step movement. Sub-pixel step movement means positioning between a pixel and neighboring pixel in order to measuring intensity of between neighboring pixels. In other words, this method finds interpolation intensity between neighboring pixels. So this can make phase step smaller than πv. To perform this method we applied the Linnik type Phase Shift Interferometry that uses a nanometer resolution XY stage with piezoelectric actuator and a monolithic flexure hinge mechanism.
