Hot forming of a large deformable mirror facesheet

Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation V, pp. 25

Abstract

Conventionally, facesheets for deformable mirrors (DM) are manufactured through grinding, polishing and finishing of a piece of optical glass. Due to the amount of material that needs to be removed, the required surface form errors and the complex handling of the fragile product throughout all manufacturing steps, this is a lengthy, risky and expensive process. For the 620mm-diameter adaptive secondary mirror (ASM) of the University of Hawaii’s 2.2-meter telescope, we develop an alternative process where the facesheet is manufactured by hot forming (‘slumping’) of a flat glass pre-form in a mold directly to the proper shape. Since low-spatial surface form errors can be corrected with the DM actuators to a large extent, only the mid/high-spatial errors beyond the period of the actuator spacing are considered critical. Through accurate modeling, and an iterative approach of hot-forming, metrology and adjustment of process parameters, the forming process is optimized to obtain the near-final shape. This approach limits the amount of required finishing operations, resulting in a facesheet meeting specifications at significantly reduced cost. We present results for the modeling & simulations, and the progress in manufacturing of this ASM facesheet.

Authors 9

1. Wouter A. Jonker

   Netherlands Organisation for Applied Scientific Research

   Affiliation as printed

   TNO Space&Scientific Instrumentation (Netherlands)

2. Stefan Kuiper

   Netherlands Organisation for Applied Scientific Research

   Affiliation as printed

   TNO Space&Scientific Instrumentation (Netherlands)

3. Fred Kamphues

   Netherlands Organisation for Applied Scientific Research

   Affiliation as printed

   TNO Space&Scientific Instrumentation (Netherlands)

4. Paul-Alexander Vogel Aachen Fraunhofer Institute for Production Technology

   Fraunhofer Institute for Production Technology IPT

   Affiliation as printed

   Fraunhofer Institute for Production Technology (Germany)

5. Ahn Tuan Vu Aachen Fraunhofer Institute for Production Technology

   Fraunhofer Institute for Production Technology IPT

   Affiliation as printed

   Fraunhofer Institute for Production Technology (Germany)

6. Constantin Meiners Aachen Fraunhofer Institute for Production Technology

   Fraunhofer Institute for Production Technology IPT

   Affiliation as printed

   Fraunhofer Institute for Production Technology (Germany)

7. Rik ter Horst
   Affiliation as printed

   NOVA (Netherlands)

8. Ramón Navarro
   Affiliation as printed

   NOVA (Netherlands)

9. Thomas Arnold

   Leibniz Institute of Surface Engineering

   Affiliation as printed

   Leibniz Institute of Surface Engineering (IOM) (Germany)