Abstract

To find the output intensity of an imaging system due to a spatially coherent source of narrow spectral bandwidth, the amplitude impulse response is integrated over the source, and the modulus of the result is then squared. For imaging of an incoherent source with the same spectral content, the modulus of the amplitude impulse response is squared and then integrated over the source. A system for which the coherent image intensity is zero while the incoherent intensity is unaffected is defined to be a coherence filter. The realizability of such a system is constrained by the above-mentioned properties of impulse responses. It follows from the definitions that a zero response to an unresolved coherent source located somewhere in a finite field implies a zero response to an incoherent source in the same field. Further, if a coherent source is resolved, and the impulse response of the system is space-invariant with finite support, it is shown that a coherence filter is unrealizable. However, a heuristic example suggests the possibility of approximate coherence filtering over a limited field, for a space-variant impulse response. Perfect global coherence filtering is impossible to realize however.

© 1988 Optical Society of America