Interference between two diffraction fields with a common caustic region

We describe the interference between two caustics of diffraction fields tha t are generated in a double-curve-shaped-slit interferometer. One of the sl its is obtained from the other through a projective mapping in the normal d irection. In this way the diffraction fields present the same caustic regio n because the slit functions have a common evolute. Catastrophe functions a re used for describing the optical path length of the rays involved. We sho w that the phase difference between the diffracted rays can also be conside red a catastrophe function, which permits us to describe the geometry of th e interference pattern because its singular points correspond to organized regions of the interference pattern. Experimental results are shown. (C) 19 99 Optical Society of America [S0740-3232(99)00206-9].