A simple method for testing laser beam collimation

A simple and improved method is proposed for testing laser beam collimation by a new type of grating, comprising concentric equilateral triangles and the mirror images of these triangles. Although this type of grating possesses one-dimensional periodicity in a particular direction and inherent defects in periodicity, the moiréfringe pattern formed by placing an exact replica of such a grating at its self-imaging plane shows that the self-imaging phenomenon takes care of the defects in the periodic objects.