“…A systematic study on the different kinds of exact solutions and methods for solving wave equation (6) was performed recently in (29). Here, as in (26) we suggest another method: Starting with the ansatz E (x, y, z, t) = V (x, y, z, t) exp (i(k 0 z − ω 0 t)), we separate the main phase and reduce the wave equation to 3D + 1 parabolic type one (2).…”