At this temperature, the mirror was able to flip between high and low reflectivity over a million times a second suggesting that, if it can be kept reliably at this critical temperature, gallium will make a fast (and also small and cheap) optical switch.
So far, Dr Borra has achieved a reflectivity of 50% (that is, half of the light falling on the mirror is reflected), but he is confident that he will be able to equal the 80% reflectivity of mercury.