Collimation testing based on self-imaging

It is proposed a technique to test the collimation status of a beam. The testing combines a moire beating technique with a digital technique. A self-image of the grating produced by a collimated beam is stored in the memory of the frame grabber. When a decollimation of the laser beam exists, the self-image period is modified. The digital subtraction between both self-image gratings produce a beating pattern. The beating moire fringe spacing is related to the decollimation degree of the illuminating beam. The validity of the technique is verified experimentally by using lenses of various focal lengths.