Abstract: This invention relates to unequal path interferometers which are adapted, among other possible uses, for use in detecting coherent radiation as from a laser in a packet of radiation including incoherent background radiation, which includes an unequal optical path length interferometer of the type in which portions of the radiation impinging on the interferometric component are caused to be recombined after travelling two different optical paths; the optical paths differing in length by an amount substantially greater than the coherence length of the non-coherent radiation but substantially less than the coherence length of the coherent radiation; the unequal optical path length interferometric component including a crystalline cell having anisotropic properties; circuitry for applying an ultrasonic sound wave to the crystalline cell to vary the effective index of refraction of the crystalline cell in a preselected systematic manner; a detector for detecting the intensity of the recombined portions and produci

Abstract: The present invention is directed to improvements in apparatus for analyzing coherent radiation in the presence of non-coherent ambient radiation subject to atmospheric scintillation effects, using unequal path interferometer apparatus and detector apparatus, said improvements comprising a closely packed bundle of fiber optic elements having an input face disposed adjacent the interferometer apparatus for receiving incident radiation passing therethrough, each of the elements being of a substantially smaller diameter than the atmospheric scintillation spatial structure; the said bundle of fiber optic elements having a medial portion wherein the elements are sorted or arranged into a plurality of subbundles; and said detector apparatus having a plurality of detector elements, each detector element being mounted adjacent one of the subbundles for being illuminated thereby.