One Hundred Years of Diffraction Theory

摘要

The development of diffraction theory in the last 100 years is discussed from a personal viewpoint, with emphasis on the geometrical theory of diffraction. First some early work of Kirchhoff, Rayleigh, Sommerfeld, MacDonald and others is mentioned of indicate the state of the field in the 1940's. Next the author's work during World War II is described. Then the considerations that led him to the geometrical theory of diffraction are explained, and the defects of that theory are outlined. Finally the advances in the theory since its introduction, which have remedied many of these defects, are mentioned. GTD is still being used and developed, and we may expect more progress in the future. Undoubtedly some of this progress will be along the lines indicated in the preceding section, but some will be in quite new directions. For example, corresponding to the well-known chaotic behavior of trajectories in mechanical systems, there is chaotic behavior of rays in some closed cavities and in many other cases. A method for finding the fields by ray method is lacking in these cases, and finding one is an important goal.