Frequency changes during the propagation of a light beam

Abstract The energy and therefore the frequency of electromagnetic fields are quantities which generally considered to be conserved in free space propagation. However, we observe here a varying optical wave light comes from an Arago spot. Its changes due rotational Doppler effect. More precisely, diffracted by two-dimensional asymmetric object carries orbital angular momentum that varies with distance. As rotates, experiences different shifts along It discrete quantized way as it propagates. can adjusted, without violation conservation energy. Since this phenomenon is deeply rooted diffraction process, sheds some new on still open issue.