Thin glass shells for active optics for future space telescopes

TL;DR

This paper introduces a manufacturing method for thin glass shells suitable for active optics in future space telescopes, combining hot slumping and deterministic polishing techniques to produce precise, large, segmented optical components.

Contribution

It presents a novel combination of mature technologies for fabricating large, thin glass shells with shape accuracy suitable for space telescope applications.

Findings

Successful shaping of a 130 mm glass shell prototype

Effective residual shape correction using bonnet polishing

Potential for scalable production of segmented optical shells

Abstract

We present a method for the manufacturing of thin shells of glass, which appears promising for the development of active optics for future space telescopes. The method exploits the synergy of different mature technologies, while leveraging the commercial availability of large, high-quality sheets of glass, with thickness up to few millimeters. The first step of the method foresees the pre-shaping of flat substrates of glass by replicating the accurate shape of a mold via hot slumping technology. The replication concept is advantageous for making large optics composed of many identical or similar segments. After the hot slumping, the shape error residual on the optical surface is addressed by applying a deterministic sub-aperture technology as computer-controlled bonnet polishing and/or ion beam figuring. Here we focus on the bonnet polishing case, during which the thin, deformable substrate of glass is temporary stiffened by a removable holder. In this paper, we report on the results so far achieved on a 130 mm glass shell case study.