The pump beam had a large effect on the reflectivity of the mirror, but only over a narrow range of temperatures.

ECONOMIST: Optical communications: Swish switches | The

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.

ECONOMIST: Optical communications: Swish switches | The

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.

ECONOMIST: Mirror, mirror