“…When the emitter is exactly placed at the focal point of the lens, z = |z 0 − f| = 0, the beam after the lens is properly collimated and the period of the self-images is equal to that of the grating. On the other hand, when the emitter is not exactly at the focal plane, z / = 0, the intensity distribution at a distance z 2 from the grating results in [10] I(x 3 , z 2 ) = I 0 n,n a n a n e i q 1+˛z 2 (n−n )…”