Experimental analysis of classical Arago point with white-light laser

The Arago point is a bright spot that appears at the center portion of the shadow of an obstacle such as a ball or a disk as the result of diffraction . Using this Arago point,,ve can judge the sphericity of a ball and the cir cularity of a disk, but it is difficult to distinguish the ball or the disk . To solve this problem, it is also necessary to observe the z coordinate c omponent. As a method for doing this, we rotated the disk and observed its diffraction pattern as a function of the rotation angle. By employing the w hite-light laser as the light source and a three charge coupled device (3-C CD) camera as the detector, we have observed novel phenomena, for instance the deformation of the Arago point and the distortion of the circular fring es. Also, the color (wavelength) dependence of the diffraction angle could be directly understood in a visible sense.