An imaging coherent radiometer for detecting and determining the location and wavelength of coherent radiation or coherent lack of radiation in the presence of non-coherent ambient radiation (R). The apparatus includes an unequal path interferometer (3) which divides incoming radiation (CR) containing coherent and non-coherent radiation into a first beam path and a second beam path through which a first beam and a second beam, respectively, travel. The optical path length difference between the first beam path and the second beam path are greater than the coherence length of the non-coherent radiation, but substantially less than the coherence length of the coherent radiation or coherent lack of radiation. Modulation means (10, 13) are provided to cause a predetermined difference in the optical frequencies between the first beam and the second beam proportional to a modulation signal. The first and second beams are then recombined into a recombined beam. Detecting means (4) are provided to detect the interference of the first and second beams across the entire wavefront of the recombined beam, and over the entire image of the scene being viewed. Processing means detect and determine the location and wavelength of coherent radiation or coherent lack of radiation in the scene being viewed by the apparatus. This information can then be visually displayed. Additional processing means to respond to specific coherent wavelengths or wavelength sets.
Imaging coherent radiometer.