By Stephen Battersby Transparent aluminium, a sci-fi material brought to 20th century Earth by the crew of The Enterprise in Star Trek IV: The Voyage Home, turns out to exist after all – if you see in X-rays. To create this exotic state of matter, researchers at the FLASH facility in Hamburg, Germany, took a thin piece of aluminium foil and blasted it with an X-ray laser that can generate about 10 million gigawatts of power per square centimetre. At standard temperature and pressure, solid aluminium is a lattice of ions, with a sea of free electrons in between. The FLASH beam had enough energy to knock an electron out of each ion and set it free, while the photon got absorbed in the process. Normally in a solid metal, another electron will instantly take the place of the missing one. Flash is so powerful that it can rip an electron out of every atom before others have a chance to replace them. With one electron removed, the remaining electrons around each ion settle into a different configuration, becoming too tightly bound for the laser to remove. That means the X-ray photons can’t be easily absorbed, and they fly straight through the material, making the previously opaque aluminium transparent to X-rays. This state doesn’t last long, though. Within fractions of a nanosecond, the energy pumped into the electrons is delivered to the ions, and the ions fly apart violently. “As soon as you make it, the stuff blows up,” says Justin Wark of the University of Oxford. But for an instant, Wark and his team can create a new state of matter that is as dense as ordinary solid matter, but extremely hot. “That is the sort of matter you would get towards the centre of a giant planet,” says Wark. The team hopes to study the properties of this hot, dense matter using new, more powerful lasers such as the Linac Coherent Light Source at Stanford, California. These lasers produce higher-energy X-rays that could probe the structure of the new material and measure its properties – perhaps providing some insight into the heart of Jupiter and the other giant planets. Journal reference: Nature Physics (DOI: 10.1038/NPHYS1341) More on these topics:
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