Laser flash creates exotic matter: See-through aluminium

Oxford scientists using the world’s most powerful soft X-ray laser have created an exotic new state of matter: transparent aluminium.

Once found only in the realm of science fiction, transparent aluminium carries great potential for research in such fields as planetary science and nuclear fusion.

As reported in this week’s issue of the journal Nature Physics, an international team led by Oxford University scientists used a short pulse from the FLASH laser to “knock out” a core electron from every aluminium atom in a sample … without otherwise disrupting the metal’s crystalline structure. The process made the aluminium nearly invisible to extreme ultraviolet radiation, though only for an extremely brief period: about 40 femtoseconds (a femtosecond is one billionth of one millionth of a second).

”What we have created is a completely new state of matter nobody has seen before,” said Oxford physicist Justin Wark, one of the authors of the paper. “Transparent aluminium is just the start. The physical properties of the matter we are creating are relevant to the conditions inside large planets, and we also hope that by studying it we can gain a greater understanding of what is going on during the creation of ‘miniature stars’ created by high-power laser implosions, which may one day allow the power of nuclear fusion to be harnessed here on Earth.”

The discovery was made possible with the development of a new source of radiation — the FLASH laser — that is ten billion times brighter than any synchrotron in the world (such as the UK’s Diamond Light Source). Based in Hamburg, Germany, the FLASH laser produces extremely brief pulses of soft X-ray light, each of which is more powerful than the output of a power plant that provides electricity to a whole city.

The research team focused all this power onto a spot with a diameter less than a twentieth of the width of a human hair. At such high intensities, the aluminium turned transparent.

“What is particularly remarkable about our experiment is that we have turned ordinary aluminium into this exotic new material in a single step by using this very powerful laser,” Wark said. “For a brief period, the sample looks and behaves in every way like a new form of matter. In certain respects, the way it reacts is as though we had changed every aluminium atom into silicon: it’s almost as surprising as finding that you can turn lead into gold with light!”

The researchers believe the new approach is an ideal way to create and study such exotic states of matter and will lead to further work relevant to areas as diverse as planetary science, astrophysics and nuclear fusion power.