Correlation-coefficient Based Ring-filtering Method for Centering a Non-diffracting Fringe Image

Abstract

A correlation-coefficient based ring-filtering method for centering a concentric circle fringe is proposed. The image of a non-diffracting beam, whose cross section is a concentric circle fringe, is recorded by a matrix array image sensor and downloaded onto a computer. The image is then processed by ring-filtering, with a center position in the zeroth order interference area of the non-diffracting image. Next, we change the center position of the ring-filtering and calculate the coherence coefficient between the filtered before and after images. The center of the non-diffracting image can be calculated by finding the position of the peak value of the dimensionless coherence coefficient. Because all the intensity distribution information of the non-diffracting beam is used for the calculation in the process of ring-filtering, the effect of random noise or a non-circular fringe on the centering is greatly reduced, and the center position resolution can achieve subpixel accuracy. The measurement of the spatial angle is discussed.