IMPROVEMENT IN THE REJECTION RATE OF A NULLING INTERFEROMETER BY SPATIAL-FILTERING

We propose applying the techniques of spatial filtering to the concept of interferometric coronography. In such a system, provided that the object being studied is not resolved by the individual apertures of th e interferometric array, the beams can he considered as coherent or, m ore exactly, single mode. Hence spatial filtering allows one to cleans e the beams of imperfections generated by defects on the optical compo nents of the interferometer and thus to obtain very high rejection rat es in the destructive output of the interferometer (coronographic outp ut) for an on-axis star. Numerical simulations show that the very stri ngent constraints on the optical quality of a space IR interferometer aimed at detecting extra-solar planets can be relaxed to values achiev able with current technology. In particular, we Show that the difficul ties induced by dust scattering, small micrometeorite impacts on the p rimary mirror, and high-frequency ripples of polishing residuals can b e eliminated by simple pinhole spatial filtering. The effects, however , will he less dramatic on large-scale defects such as coating defects and pointing errors in the telescopes. (C) 1997 Optical Society of Am erica.