Determination of diffractor size and shape from diffracted light

Although equations are available for predicting Fraunhofer diffraction by many obstacles or openings, they are of limited value for the inverse problem, deducing diffractor geometry from observed diffracted light. Instead of trying to invert these equations, they were used to survey the functional relations between diffractor geometry and observable patterns. Then intuitive methods were used to obtain simple approximate expressions for determining the size and general shape of simple diffractors from diffracted light. It is found that some complex diffractors diffract almost like simple diffractors of equivalent dimensions. The results reveal some of the potential capabilities and limitations of diffracted light as a source of information about unknown diffracting systems.