Liquid mirrors - Optical shop tests and contributions to the technology

Abstract

We have undertaken work to determine whether optical quality liquid mirrors are technologically feasible. We have built a testing facility, equipped with a scatterplate interferometer interfaced with a CCD for data acquisition and a microcomputer for data analysis. Extensive interferometric tests of a 1.5 m diameter i/2 liquid mirror show that it is diffraction limited as they give Strehl ratios of order 0.8 and rms surface deviations of order X/20. Direct observations of the point spread function show that the mirror does not suffer an excessive amount of scattered light. We discuss the disturbances that can limit the optical quality of liquid mirrors and how to minimize them. We discuss work that we have carried out to improve the basic technology. The purpose of this paper is not only to describe the results of optical tests but also to give technical information detailed enough that interested parties can successfully make liquid mirrors. Subject headings: instrumentation: miscellaneous — telescopes.