Abstract

Asymptotic expressions for both the Green's function and the wave propagator of scalar diffraction theory are derived in terms of the point characteristic of geometrical optics. These expressions are valid when the refractive index varies slowly on the scale of a wavelength. They are derived directly from the wave equation by using coincidence limits to select unique forms. The relationship between the Green's function and the propagator is discussed along with a careful treatment of their interpretation and validity.

© 1997 Optical Society of America

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