The quest to create nuclear fusion may have come a step closer when scientists heated solid matter to two million degrees with the world's most powerful X-ray laser, a study reported Wednesday.

A team of researchers working at the SLAC National Accelerator Laboratory in Menlo Park, California used the rapid-fire laser -- a billion times brighter that any other man-made X-ray source -- to flash-heat a miniscule piece of aluminum foil.

In so doing, they created a form of plasma known as "hot dense matter," reaching temperatures hotter than two million degrees Celsius (3.6 million degrees Fahrenheit).

The whole process lasted less than a trillionth of a second.

Gas-like plasma is often called the fourth state of matter after solids, liquids and gases. While uncommon on Earth, it makes up over 99 percent of the visible universe, including the interior of stars such as the Sun.

"Making extremely hot, dense matter is important scientifically if we are ultimately to understand the conditions that exist inside stars and at the center of giant planets within our own solar system," said lead author Sam Vinko, a researcher at the University of Oxford.

Scientists have long been able to create electrically-charged plasma by heating gases, which can ripe away electrons from their atoms.

But up to now no tools existed for doing the same thing at solid densities that cannot be penetrated by conventional laser beams.

In the experiments, reported in the journal Nature, scientists used ultra-short wavelengths of X-ray laser light to blast the aluminum foil and create, for the first time, a uniform patch of plasma, a cube about one thousandth of a centimetre per side.

The results will be measured against theories and computer simulations as to how hot, dense matter behaves.

And it should help understand -- and perhaps one day recreate -- nuclear fusion, long heralded as a potentially unlimited and clean source of energy, the researchers said.

"Linac Coherent Light Source (LCLS) is really going to revolutionise the field, in my view," said co-author Justin Wark, also at Oxford, referring to the laser used in the experiment.

There are currently two main paths towards making fusion energy.

One uses large-scale magnetic fields, the approach adopted by the International Thermonuclear Experimental Reactor (ITER) in France, set to become operational in 2019.

The National Ignition Facility in the United States (NIF), by contrast, is one of several experimental facilities to use very high-energy optical lasers to achieve the same end.