Diffractive changes in the frequency spectrum of propagating radiation (the Wolf effect)

The propagation of a nonmonochromatic wave beam through a lossless dispersive medium is treated in the paraxial approximation. The frequency spectrum of the beam changes in the process because of the finite dimensions and the imperfect spatial coherence of the source. These changes are analyzed. A physical model is offered to explain the basic features of this effect. Methods for compensating for it are discussed. Possibilities for utilizing it are also discussed. The physical meaning of the "scaling law" is discussed.