Interferometric coupling of the Keck telescopes with single-mode fibers.

Here we report successful interferometric coupling of two large telescopes with single-mode fibers. Interference fringes were obtained in the 2- to 2.3-micrometer wavelength range on the star 107 Herculis by using the two Keck 10-meter telescopes, each feeding their common interferometric focus with 300 meters of single-mode fibers. This experiment demonstrates the potential of fibers for future kilometric arrays of telescopes and is the first step toward the 'OHANA (Optical Hawaiian Array for Nanoradian Astronomy) interferometer at the Mauna Kea observatory in Hawaii. It opens the way to sensitive optical imagers with resolutions below 1 milli-arc second. Our experimental setup can be directly extended to large telescopes separated by many hundreds of meters.

Diffraction by a half-plane: a generalization of the Fresnel diffraction theory.

A generalization of the Fresnel approximation in diffraction theory is proposed. The phase term in the diffraction integral is approximated by a parabolic variation, not by a binomial expansion but rather by matching up at the critical points for asymptotic evaluation of the integral. The method provides a correction to the optical coordinates of the Fresnel diffraction theory that extends its region of validity. It is applied to diffraction of an inclined plane wave by a half-plane.