Method for edge detection based on phase jump in a differential interferometer

We describe a new method for edge detection that uses polarization mixing i n a differential heterodyne interferometer. When one of the focused beams o f the interferometer scans across an edge, a phase jump of 180 degrees take s place in the very small region of the edge if certain conditions are sati sfied. We call this phenomenon phase jump. The conditions in which phase ju mp can occur are given. The theoretical analysis shows that the slope of a phase jump is infinite and is not affected by step height, the vibration of the sample, or the intensity variation of the light source. Therefore phas e jump can be used as the precise index for edge detection. The experimenta l results show good agreement with the theoretical analysis. (C) 1999 Optic al Society of America.