Fast Positioning of Zero Path Difference of White Light Interference Based on Image Processing

This topic is based on the image processing method to realize the rapid positioning of the zero path difference of white light interference. The more stable and compact Mirau objective lens is used in the interference light path. The objective lens is driven by a stepping motor to change the size of the optical path difference to obtain interference images at different positions. The interference image is transformed into a spectrum signal by Fourier transform, and the high frequency signal is increased and the low frequency signal is reduced through a certain evaluation function, and the interference situation is quantitatively described. The position with the largest evaluation function value is the position of in-focus. Since the interference signals at different positions will be superimposed and affect the focusing judgment, we adopt the method of sub-area focusing to process the upper and lower surfaces of the groove separately to achieve precise focusing. For the step measurement of the 1-word part of a dime coin, the measurement result of the white light interferometer is 17um, and the in-focus position of the upper and lower surfaces measured by this method is 15um, which is basically consistent with the actual value.