January 26, 2012
Scientists Create World’s Most Powerful X-ray Laser
Creating and observing super-hot solid plasma could lead to a greater understanding of fusion processes.
In two separate studies, the world´s most powerful X-ray laser has been used to build the first atomic X-ray laser pulse, as well as to superheat and control a clump of 2-million-degree matter. The atomic laser could be used to watch biological molecules at work, while the creation of hot dense matter could be used to understand the processes of nuclear fusion.
The achievement, reported Wednesday in the journal Nature, represents a giant step forward in the quest to understand the most extreme matter found in the hearts of stars and giant planets.
The researchers aimed SLAC's Linac Coherent Light Source (LCLS) at a capsule of neon gas, setting off an avalanche of X-ray emissions to create the first-ever "atomic X-ray laser”, with pulses a billion times brighter than those of any X-ray source in the world.
The scientists used the rapid-fire pulses to flash-heat a tiny piece of aluminum foil, creating what is known as "hot dense matter”, and measured the temperature of this solid plasma, finding it to be about 3.6 million degrees Fahrenheit (2 million degrees Celsius).
The entire process took less than a trillionth of a second.
"X-rays give us a penetrating view into the world of atoms and molecules," said lead researcher Nina Rohringer, a physicist and group leader at the Max Planck Society's Advanced Study Group in Hamburg, Germany.
"We envision researchers using this new type of laser for all sorts of interesting things, such as teasing out the details of chemical reactions or watching biological molecules at work," said Rohringer, who collaborated with researchers from SLAC, DOE's Lawrence Livermore National Laboratory and Colorado State University.
"The shorter the pulses, the faster the changes we can capture. And the purer the light, the sharper the details we can see,” said Rohringer.
Indeed, the powerful laser created by Rohringer and colleagues generated the shortest, purest X-ray pulses ever achieved, which could also help experiments aimed at recreating the nuclear fusion process that powers the sun.
The atomic X-ray laser fulfills a 1967 prediction that X-ray lasers could be made in the same manner as many visible-light lasers — by inducing electrons to fall from higher to lower energy levels within atoms, releasing a single color of light in the process.
Before 2009, when LCLS became operational, no X-ray source was powerful enough to create this type of laser.
To create the current atom laser, LCLS's powerful X-ray pulses knocked electrons out of the inner shells of many of the neon atoms in the capsule. When other electrons fell in to fill the holes, about one in 50 atoms responded by emitting a photon in the X-ray range, which has a very short wavelength.
Those X-rays then stimulated neighboring neon atoms to emit more X-rays, creating a domino effect that amplified the laser light 200 million times.
Although LCLS and the neon capsule are both lasers, they create light in different ways and emit light with different attributes. The LCLS passes high-energy electrons through alternating magnetic fields to trigger production of X-rays -- its X-ray pulses are brighter and much more powerful.
The atomic laser's pulses are only one-eighth as long and their color is much more pure, qualities that will enable it to illuminate and distinguish details of ultrafast reactions that had been impossible to see before.
"This achievement opens the door for a new realm of X-ray capabilities," said John Bozek, LCLS instrument scientist.
"Scientists will surely want new facilities to take advantage of this new type of laser."
For example, researchers envision using both LCLS and atomic laser pulses in a synchronized one-two punch: The first laser triggers a change in a sample under study, while the second records with atomic-scale precision any changes that occurred within a few quadrillionths of a second.
Rohringer said her future work would include attempts to create even shorter-pulsed, higher-energy atomic X-ray lasers using oxygen, nitrogen or sulfur gas.
Image 1: This photograph shows the interior of a Linac Coherent Light Source SXR experimental chamber, set up for an investigation to create and measure a form of extreme, 2-million-degree matter known as “hot, dense matter.” The central part of the frame contains the holder for the material that will be converted by the powerful LCLS laser into hot, dense matter. To the left is an XUV spectrometer and to the right is a small red laser set up for alignment and positioning. (Photo courtesy University of Oxford/Sam Vinko)
Image 2: A powerful X-ray laser pulse from SLAC National Accelerator Laboratory's Linac Coherent Light Source comes up from the lower-left corner (shown as green) and hits a neon atom (center). This intense incoming light energizes an electron from an inner orbit (or shell) closest to the neon nucleus (center, brown), knocking it totally out of the atom (upper-left, foreground). In some cases, an outer electron will drop down into the vacated inner orbit (orange starburst near the nucleus) and release a short-wavelength, high-energy (i.e. "hard") X-ray photon of a specific wavelength (energy/color) (shown as yellow light heading out from the atom to the upper right along with the larger, green LCLS light). X-rays made in this manner then stimulate other energized neon atoms to do the same, creating a chain-reaction avalanche of pure X-ray laser light amplified by a factor of 200 million. While the LCLS X-ray pulses are brighter and more powerful, the neon atomic hard X-ray laser pulses have one-eighth the duration and a much purer light color. This new laser will enable more precise investigations into ultrafast processes and chemical reactions than had been possible before, ultimately opening the door to new medicines, devices and materials. Illustration by Gregory M. Stewart, SLAC National Accelerator Laboratory
On the Net:
- DOE SLAC National Accelerator Laboratory
- Max Planck Society
- Lawrence Livermore National Laboratory
- Colorado State University