Scientists Create First Atomic X-Ray Laser

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). (Credit: Illustration by Gregory M. Stewart, SLAC National Accelerator Laboratory)

Scientists working at the U.S. Department of Energy's (DOE) SLAC National Accelerator Laboratory have created the shortest, purest X-ray laser pulses ever achieved, fulfilling a 45-year-old prediction and opening the door to a new range of scientific discovery.

The researchers, reporting in Nature, 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 world's first "atomic X-ray laser."

"X-rays give us a penetrating view into the world of atoms and molecules," said physicist Nina Rohringer, who led the research. A group leader at the Max Planck Society's Advanced Study Group in Hamburg, Germany, Rohringer collaborated with researchers from SLAC, DOE's Lawrence Livermore National Laboratory and Colorado State University.

"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," she added. "The shorter the pulses, the faster the changes we can capture. And the purer the light, the sharper the details we can see."

The new 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. But until 2009, when LCLS turned on, no X-ray source was powerful enough to create this type of laser.

To make the atom laser, LCLS's powerful X-ray pulses -- each a billion times brighter than any available before -- 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, and the second records with atomic-scale precision any changes that occurred within a few quadrillionths of a second.

In future experiments, Rohringer says she will try to create even shorter-pulsed, higher-energy atomic X-ray lasers using oxygen, nitrogen or sulfur gas.

Additional authors included Richard London, Felicie Albert, James Dunn, Randal Hill and Stefan P. Hau-Riege from Lawrence Livermore National Laboratory (LLNL); Duncan Ryan, Michael Purvis and Jorge J. Rocca from Colorado State University; and Christoph Bostedt from SLAC.

The work was supported by Lawrence Livermore National Laboratory's Laboratory Directed Research and Development Program. Authors Roca, Purvis and Ryan were supported by the DOE Office of Science. LCLS is a national scientific user facility operated by SLAC and supported by DOE's Office of Science.

Story Source:

The above story is reprinted from materials provided by DOE/SLAC National Accelerator Laboratory.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

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Journal Reference:

1. Nina Rohringer, Duncan Ryan, Richard A. London, Michael Purvis, Felicie Albert, James Dunn, John D. Bozek, Christoph Bostedt, Alexander Graf, Randal Hill, Stefan P. Hau-Riege, Jorge J. Rocca. Atomic inner-shell X-ray laser at 1.46 nanometres pumped by an X-ray free-electron laser. Nature, 2012; 481 (7382): 488 DOI:10.1038/nature10721

Lab Mimics Jupiter's Trojan Asteroids Inside a Single Atom

Rice University graduate student Shuzhen Ye used an ultraviolet laser to create a Rydberg atom in order to study the orbital mechanics of electrons. (Credit: Jeff Fitlow/Rice University)

ScienceDaily  — Rice University physicists have gone to extremes to prove that Isaac Newton's classical laws of motion can apply in the atomic world: They've built an accurate model of part of the solar system inside a single atom of potassium.

In a new paper published this week in Physical Review Letters, Rice's team and collaborators at the Oak Ridge National Laboratory and the Vienna University of Technology showed they could cause an electron in an atom to orbit the nucleus in precisely the same way that Jupiter's Trojan asteroids orbit the sun.

The findings uphold a prediction made in 1920 by famed Danish physicist Niels Bohr about the relationship between the then-new science of quantum mechanics and Newton's tried-and-true laws of motion.

"Bohr predicted that quantum mechanical descriptions of the physical world would, for systems of sufficient size, match the classical descriptions provided by Newtonian mechanics," said lead researcher Barry Dunning, Rice's Sam and Helen Worden Professor of Physics and chair of the Department of Physics and Astronomy. "Bohr also described the conditions under which this correspondence could be observed. In particular, he said it should be seen in atoms with very high principal quantum numbers, which are exactly what we study in our laboratory."

Bohr was a pioneer of quantum physics. His 1913 atomic model, which is still widely invoked today, postulated a small nucleus surrounded by electrons moving in well-defined orbits and shells. The word "quantum" in quantum mechanics derives from the fact that these orbits can have only certain well-defined energies. Jumps between these orbits lead to absorption or emission of specific amounts of energy termed quanta. As an electron gains energy, its quantum number increases, and it jumps to higher orbits that circle ever farther from the nucleus.

In the new experiments, Rice graduate students Brendan Wyker and Shuzhen Ye began by using an ultraviolet laser to create a Rydberg atom. Rydberg atoms contain a highly excited electron with a very large quantum number. In the Rice experiments, potassium atoms with quantum numbers between 300 and 600 were studied.

"In such excited states, the potassium atoms become hundreds of thousands of times larger than normal and approach the size of a period at the end of a sentence," Dunning said. "Thus, they are good candidates to test Bohr's prediction."

He said comparing the classical and quantum descriptions of the electron orbits is complicated, in part because electrons exist as both particles and waves. To "locate" an electron, physicists calculate the likelihood of finding the electron at different locations at a given time. These predictions are combined to create a "wave function" that describes all the places where the electron might be found. Normally, an electron's wave function looks like a diffuse cloud that surrounds the atomic nucleus, because the electron might be found on any side of the nucleus at a given time.

Dunning and co-workers previously used a tailored sequence of electric field pulses to collapse the wave function of an electron in a Rydberg atom; this limited where it might be found to a localized, comma-shaped area called a "wave packet." This localized wave packet orbited the nucleus of the atom much like a planet orbits the sun. But the effect lasted only for a brief period.

"We wanted to see if we could develop a way to use radio frequency waves to capture this localized electron and make it orbit the nucleus indefinitely without spreading out," Ye said.

They succeeded by applying a radio frequency field that rotated around the nucleus itself. This field ensnared the localized electron and forced it to rotate in lockstep around the nucleus.

A further electric field pulse was used to measure the final result by taking a snapshot of the wave packet and destroying the delicate Rydberg atom in the process. After the experiment had been run tens of thousands of times, all the snapshots were combined to show that Bohr's prediction was correct: The classical and quantum descriptions of the orbiting electron wave packets matched. In fact, the classical description of the wave packet trapped by the rotating field parallels the classical physics that explains the behavior of Jupiter's Trojan asteroids.

Jupiter's 4,000-plus Trojan asteroids -- so called because each is named for a hero of the Trojan wars -- have the same orbit as Jupiter and are contained in comma-shaped clouds that look remarkably similar to the localized wave packets created in the Rice experiments. And just as the wave packet in the atom is trapped by the combined electric field from the nucleus and the rotating wave, the Trojans are trapped by the combined gravitational field of the sun and orbiting Jupiter.

The researchers are now working on their next experiment: They're attempting to localize two electrons and have them orbit the nucleus like two planets in different orbits.

"The level of control that we're able to achieve in these atoms would have been unthinkable just a few years ago and has potential applications in, for example, quantum computing and in controlling chemical reactions using ultrafast lasers," Dunning said.

The research was funded by the National Science Foundation, the Robert A. Welch Foundation, the Austrian Science Fund and the Department of Energy. Paper co-authors include S. Yoshida of the Vienna University of Technology; C.O. Reinhold of Oak Ridge National Laboratory and the University of Tennessee; and J. Burgdörfer of Vienna University of Technology and the University of Tennessee.

Story Source:

The above story is reprinted from materials provided by Rice University.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

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Journal Reference:

1. B. Wyker, S. Ye, F. Dunning, S. Yoshida, C. Reinhold, J. Burgdörfer. Creating and Transporting Trojan Wave Packets. Physical Review Letters, 2012; 108 (4) DOI:10.1103/PhysRevLett.108.043001

Atomic Gardens, the Biotechnology of the Past, Can Teach Lessons About the Future of Farming

When radioactive tomatoes were the crop of the future
Atomic Seeds Life Magazine via Pruned

One look at the wedge-shaped rows of plants and anyone could tell the circular garden was not grown under normal conditions. Plants sown in concentric circles displayed wildly different vitality and viability.

The innermost circle of plants, gathered around a central pole, were dead; slightly farther away, the plants were stunted and tumor-ridden; and past that, the plants may have looked right, but possessed strange new mutations.

It was the latter part of the archetypal “gamma garden” that most interested plant researchers in the 1950s and 1960s. The central pole contained a radioactive source, commonly cobalt-60, so that scientists could see how the gamma rays affected plants.

Before scientists learned how to modify genes, they induced mutations with radiation. It was a sincere effort to feed the world, and amaze home gardeners, by modifying plants to have desirable traits.

Nanotechnologist Paige Johnson shares the history of atomic gardening on her blog, Garden History Girl. Writer Alexander Trevi interviewed Johnson for his own blog, Pruned.

“If we think of modern GM as taking a scalpel to the genome, mutation breeding by irradiation was a hammer,” she says. The full interview is well worth a read; click through to it here.

It’s an interesting tale in light of radiation and food safety concerns after the Japanese nuclear disaster. But there are also some interesting parallels between atomic gardening and 21st-century biotechnology, which also promises to feed the world by modifying plants to have new traits. The promises, and the controversies, feel very familiar.

Back in the 1960s, scientists bombarded plants with gamma radiation hoping to see beneficial changes in the plants’ structure and yield. Advocates included entrepreneur C.J. Speas and Englishwoman Muriel Howorth, who started the Atomic Gardening Society to promote mutated varieties. Johnson describes a dinner party in which Howorth served “NC 4x,” North Carolina 4th generation X-rayed peanuts that were produced from seeds exposed to 18,500 roentgen units of X-rays. After the party, Howorth planted the irradiated seeds and they grew like magic beanstalks.

Journalists and sightseers came to visit the mutant plant; garden writer Beverley Nichols called the peanut the “most sensational plant in Britain.”

“To me it had all the romance of something from outer space. It is the first ‘atomic’ peanut. It is a lush, green plant and gives you a strange, almost alarming sense of thrusting power and lusty health. It holds a glittering promise in its green leaves, the promise of victory over famine,” she wrote, as recounted on Johnson’s blog.

As with modern biotechnology, industry was the main driver behind the new plant modifications. Two modern cultivars are the result of atomic gardening, Johnson says — most of the world's mint oil, used in toothpaste, chewing gum and more, comes from the “Todd's Mitcham” peppermint cultivar, which is resistant to a fungus. It was produced in radiation gardens at Brookhaven National Laboratory. And the “Rio Star” grapefruit varietal, which Johnson says accounts for three-fourths of grapefruit production in Texas, is another atomic mutant bred for its dark red flesh and juice.

Gamma garden research was conducted in the U.S., Sweden, India and other countries in the 1960s, leading to untold numbers of new plant varieties. But s far as Johnson can tell, the entrepreneur Speas was the only source for home gardeners to buy irradiated seeds. Seed packets depicted robust flowers and vegetables, calling them “atomic-energized” and offering an interesting definition of what radiation does — “gamma rays tend to shake up the normal balanced system of the embryo inside the plant.”

Atomic Energized Poppy: The seed packet advises gardeners that it may take more than a year for mutations to manifest themselves, and therefore not to destroy stunted plants: “The stunted plants may contain desirable changes when they again regain their hereditary balance in subsequent generations.”  Paige Johnson via Pruned

Eventually, as scientists and the public grew to understand the dangers posed by radiation exposure, gamma gardens fell out of favor. The notion of irradiated plants feeding a hungry world soon wilted, too.

Decades later, scientists would figure out how to make much more precise mutations, inserting new genes and switching them on to make plants do things they couldn’t do before. But this method has its own detractors, some of whom would argue genetic modification is just as bad for health and the environment as radioactivity research.

We know much more about biology today than we did in the 1960s. But will future generations look back on genetic modification like we reflect on atomic gardens, with an amused sense of nostalgia illuminated by hindsight?

View the original article here