Detection Of Hidden Diffractors By Coherence Measurements

The scattering of partially coherent radiation by structures such as diffraction gratings is analysed theoretically. The far-zone intensity and degree of coherence patterns are obtained in terms of relevant source parameters such as coherence length, beam width, phase curvature, and the properties of the diffracting structure. Particularly noteworthy is the fact that for relatively low source correlation lengths, far-zone coherence measurements can detect evidence of the diffracting structures even though the radiant intensity may be completely diffuse. This phenomenon has potential application to the coding and detection of optical information. Recent experiments do indeed corroborate these predictions.