What's the Matter

27 Jul 09 - Oxford scientists have created a transparent form of aluminum by bombarding the metal with the world’s most powerful soft X-ray laser. ‘Transparent aluminum’ previously only existed in science fiction, featuring in the movie Star Trek IV, but the real material is an exotic new state of matter with implications for planetary science and nuclear fusion.

An international team, led by Oxford University scientists, report that a short pulse from the FLASH laser ‘knocked out’ a core electron from every aluminum atom in a sample without disrupting the metal’s crystalline structure. This turned the aluminum nearly invisible to extreme ultraviolet radiation.

''What we have created is a completely new state of matter nobody has seen before. We have turned ordinary aluminum into this exotic new material in a single step by using this very powerful laser. For a brief period the sample looks and behaves in every way like a new form of matter." said Professor Justin Wark of Oxford University’s Department of Physics, one of the authors of the paper.

The discovery was made possible with the development of a new source of radiation that is ten billion times brighter than any synchrotron in the world. The FLASH laser, based in Hamburg, Germany, 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 Oxford team, along with their international colleagues, focused all this power down into a spot with a diameter less than a twentieth of the width of a human hair. At such high intensities the aluminum turned transparent.

Whilst the invisible effect lasted for only an extremely brief period – an estimated 40 femtoseconds (A femtosecond is one millionth of a nanosecond or 10 to the minus 15th of a second. For comparison, a millisecond is one thousandth of a second).

Professor Wark added: ‘What is particularly remarkable about our experiment is that A report of the research, ‘Turning solid aluminium transparent by intense soft X-ray photoionization’, is published in Nature Physics.