Creating Dark Lines in Space with Linear Zone Plates

Zone plates are complex patterns that are alternately opaque and transparent; they use diffraction to focus light, unlike lenses, which use refraction. Linear zone plates produce a focal line rather than a focal spot. Conventional linear zone plates produce bright foci, but in this project dark foci created by zone plates with pi-phase jumps, which are abrupt shifts in transparency, were studied. Zone plate patterns were calculated with the Mathematica computer program, and an outside company photographically produced the corresponding zone plates on 35 mm slides. The zone plates were tested by illuminating them with an attenuated laser beam and observing the resulting diffraction patterns with a CCD camera.