Gallium liquid mirrors: Basic technology, optical-shop tests and observations

We have investigated the use of gallium and low-melting-temperature gallium alloys for liquid mirrors. They have advantageous characteristics with respect to mercury. Simple knife-edge and Ronchi optical tests indicate that gallium mirrors have optical qualities similar to those of mercury mirrors. We have observed stars with a 1-m diameter liquid-mirror telescope that used a gallium-indium ahoy. The instrument operated satisfactorily, within the limitations of a very simple telescope and instrumentation. Arguably, our most interesting finding is that the high melting temperature of gallium is not an obstacle since our experiments show that it is easy to supercool in large volumes and quite stable in the supercooled state. Furthermore, eutectic alloys of gallium have significantly lower melting temperatures than pure gallium and are also easy to supercool and stable in the supercooled state. The results of our experiments are encouraging and warrant further, more rigorous, continuation of this work.