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. © 2008 ESO.