APPARATUS FOR DETECTING THE PRESENCE OF COHERENT RADIATION IN THE PRESENCE OF NON-COHERENT AMBIENT RADIATION

摘要

The present invention is directed to an improved unequal path interferometer which is a particularly adapted, among many other possible uses, for detecting coherent radiation in the presence of non-coherent ambient radiation, which comprises 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 comprising a liquid crystal cell having dielectric anisotropic properties; elements for applying a time varying electric field vector to the liquid crystal cell to vary the effective index of refraction of the liquid crystal cell in a preselected systematic manner; and elements for detecting the intensity of the recombined portions and producing a signal representative thereof, said signal having a variable component caused by the varying constructive and destructive interference of the recombined coherent radiation components, while the recombined non-coherent radiation components produce only a substantially steady background signal.