Binary crossing a linear array of telescopes

The movies BinaryCrossing1.avi and BinaryCrossing2.avi (1.6MB each) or BinaryCrossing1.mpg and BinaryCrossing2.mpg (0.6MB each) are from a laboratory experiment demonstrating a combination of twelve beams in an interferometer, after the delay lines. An arc lamp illuminates two adjacent pinholes, simulating a binary, normal to the paper (Figure, a). Also normal to the paper, an array of lenslets is masked to pass only a strip of 12, where each beam is weakly focusing (namely the wave fronts are not planar). This is in order to show the separate beams. This strip is extended in the paper plane by a cylindrical telephoto, and after passing through a 90⁰ shear interferometer, is re-imaged on a camera. The Sagnac interferometer (Figure, b). contains one beam splitter and four mirrors, one outside the paper plane, to rotate the images mutually. The pinholes are moved across the plane of the paper, to simulate meridian crossing. Imperfections in the image are due to the simple optics used; with better components many more beams could be combined. A liquid crystal retarder allows cancellation of residual polarisation effects, but is not required. No polarizers or colour filters were used.