Double Knife-Edge Diffraction and Ray Theory

The signal produced by the diffraction of two knife-edges is determined in a high-frequency approximation and the resulting field ia compared with the predictions of ray theory. It is found that ray theory gives the field accurately provided that the inoident field can be expanded in a certain way near the edge and that suitable modifications are introduced if this expansion does not hold over the whole of the aperture. An example is given to show that ray theory is not correct when such an expansion of the incident field is not available near the edge. The extension of the theory to more than two knife-edges is briefly discussed. 1.