One hundred years of diffraction theory

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 to 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.