Stressed mirror polishing 2: Fabrication of an off-axis section of a paraboloid

Abstract

A mirror has been fabricated with the shape of an off-axis section of a paraboloid by grinding and polishing a sphere into a prestressed blank. The applied stresses were then removed allowing the mirror to spring into the desired paraboloidal shape. The 36-cm diam off-axis section deviated 9.9-microm rms from the polished sphere. The final surface deviated 0.03-microm rms from the desired off-axis section.

Active optics: off axis aspherics generation for high contrast imaging

“…In the case of off axis parabolas (OAP) and off-axis aspherics (OAA), the optical surface is not only a sphere and a simple mode, but combines several modes depending on the parameters defining the surface: the F-ratio of the parent aspheric and the OAA, the off axis distance and the conic constant in case of an OAA. Lubliner & Nelson [19] [20] described the analytical equations giving the asphericities or Zernike modes to be generated on a sphere versus these parameters, in the frame of the manufacturing of Keck's primary mirrors segments. Two times 36 segments plus spares have been manufactured with this technique and then finished using Ion Beam (IBF) in order to remove the final HiF on the surface.…”

Development of the Thirty-Meter Telescope Project

“…The correction bandwidth is 2 Hz. Each of the components of the segmented primary mirror required significant new technology developments [1][2][3] . Because the individual segments are small, they can be much thinner than a large monolithic mirror, and the weight of all the segments can be much smaller than the equivalent diameter monolithic mirror, greatly simplifying the telescope structure needed to support and control the mirror shape.…”

Optical design and active optics methods in astronomy

“…Nelson et al 18) applied the method to the construction of 36 segments of the primary mirror. The stress figuring aspherization process of 1.8m segments used circular Zerodur meniscus.…”