Retrospective of Roland Shack's global view of diffraction [Invited]

In April of 1972, Professor Roland Shack presented a series of four colloquium talks at the Optical Sciences Center at the University of Arizona in which he reformulated scalar diffraction theory in terms of the direction cosines of the propagation vectors of the angular spectrum of plane waves described by the Fourier integral transform of the diffracting aperture. The fourth lecture, entitled Radiometry and Lambert's Law, described diffuse reflectance and surface scatter phenomena as merely a diffraction phenomenon caused by random phase variations in the system pupil function. In 1974, he elegantly condensed these four lectures into a single colloquium talk entitled A Global View of Diffraction. This paper is intended to provide a compilation showing the further development of that work over the last 46 years.