Tiltable rotating liquid mirrors: a progress report

Abstract

Context. We give a progress report on tiltable, nanoengineered, rotating liquid mirrors, which were discussed in previous papers. Aims. We want to develop the technology, improve reflectivities and user-friendliness. The ultimate goal is to demonstrate high-quality liquid mirrors that can be tilted by a few tens of degrees. Methods. We coated hydrophilic liquid substrates that have poor reflectivities with a reflective layer of self-assembling metallic nanoparticles. We analyzed the wavefronts of 1-m diameter mirrors with Ronchi tests, knife-edge tests and point-spread functions (PSFs).Results. There is significant improvement over previous work where the reflecting layer was deposited on hydrophobic oils. While previous work only demonstrated tilted low-reflectivity mirrors, we now test a high-reflectivity 1-m diameter liquid mirror tilted by 45 arcmin. Conclusions. It is considerably easier to coat hydrophilic liquids than hydrophobic ones. We have reached a significant milestone by demonstrating a tilted, highly reflective, liquid mirror. Although this is still an immature technology, it is near the stage where it could be used in astronomy. The remaining technical challenges, for which we propose solutions, are not fundamental and could be overcome with additional work. This will be a worthwhile undertaking, considering the very low cost of liquid mirrors.

Magnetically Deformable Liquid Mirrors from Surface Films of Silver Nanoparticles

“…The majority of commercial ferrofluids, however, are oil-based and therefore do not exhibit the high surface energies required for the facile spreading of the nanoparticles as a surface film. [15,32,33] Aqueous ferrofluids are known [34][35][36] but are not suitable for the preparation of stable magnetic mirrors because of the relatively rapid evaporation of water. In order to meet, simultaneously, the criteria of low vapour pressure and high surface tension, we have identified ethylene glycol as an appropriate carrier liquid.…”

Reflective Liquid-Like Films of Silver Nanoparticles

“…On the other hand, the films reveal the macroscopic properties of a liquid [2]. Owing to these special properties of the films, they can be used as potential materials to form liquid mirrors [3][4][5].…”

Ethylene Glycol Based Ferrofluid for the Fabrication of Magnetically Deformable Liquid Mirrors

“…Highly reflective surface films of silver nanoparticles can be spread on water, ethylene glycol, and several other hydrophilic liquids . The majority of commercial ferrofluids, however, are oil based and therefore do not have sufficiently high surface energies to permit the facile spreading of surface films.…”