World's Most Powerful X-Ray Laser Creates 2-Million-Degree Matter

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. (Credit: Photo courtesy of University of Oxford/Sam Vinko)

Researchers working at the U.S. Department of Energy's (DOE) SLAC National Accelerator Laboratory have used the world's most powerful X-ray laser to create and probe a 2-million-degree piece of matter in a controlled way for the first time. This feat, reported inNature, takes scientists a significant step forward in understanding the most extreme matter found in the hearts of stars and giant planets, and could help experiments aimed at recreating the nuclear fusion process that powers the sun.

The experiments were carried out at SLAC's Linac Coherent Light Source (LCLS), whose rapid-fire laser pulses are a billion times brighter than those of any X-ray source before it. Scientists used those pulses to flash-heat a tiny piece of aluminum foil, creating what is known as "hot dense matter," and took the temperature of this solid plasma -- about 2 million degrees Celsius. The whole process took less than a trillionth of a second.

"The LCLS X-ray laser is a truly remarkable machine," said Sam Vinko, a postdoctoral researcher at Oxford University and the paper's lead author. "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 and beyond."

Scientists have long been able to create plasma from gases and study it with conventional lasers, said co-author Bob Nagler of SLAC, an LCLS instrument scientist. But no tools were available for doing the same at solid densities that cannot be penetrated by conventional laser beams.

"The LCLS, with its ultra-short wavelengths of X-ray laser light, is the first that can penetrate a dense solid and create a uniform patch of plasma -- in this case a cube one-thousandth of a centimeter on a side -- and probe it at the same time," Nagler said.

The resulting measurements, he said, will feed back into theories and computer simulations of how hot, dense matter behaves. This could help scientists analyze and recreate the nuclear fusion process that powers the sun.

"Those 60 hours when we first aimed the LCLS at a solid were the most exciting 60 hours of my entire scientific career," said Justin Wark, leader of the Oxford group. "LCLS is really going to revolutionize the field, in my view."

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

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Journal Reference:

1. S. M. Vinko, O. Ciricosta, B. I. Cho, K. Engelhorn, H.-K. Chung, C. R. D. Brown, T. Burian, J. Chalupský, R. W. Falcone, C. Graves, V. Hájková, A. Higginbotham, L. Juha, J. Krzywinski, H. J. Lee, M. Messerschmidt, C. D. Murphy, Y. Ping, A. Scherz, W. Schlotter, S. Toleikis, J. J. Turner, L. Vysin, T. Wang, B. Wu, U. Zastrau, D. Zhu, R. W. Lee, P. A. Heimann, B. Nagler, J. S. Wark. Creation and diagnosis of a solid-density plasma with an X-ray free-electron laser. Nature, 2012; DOI: 10.1038/nature10746

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.

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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

Ultrafast Magnetic Processes Observed 'Live' Using an X-Ray Laser

Detail of the structure of cupric oxide (CuO). The copper atoms (green) carry a magnetic moment, behaving like small compass needles. The direction of the magnetic moment is illustrated by a red arrow. A point means that the arrow is pointing out of the surface (we are looking at its sharp end), a cross shows that the arrow is pointing into the surface (we are looking at its tail end). The magnetic structure changes significantly as the temperature increases above 213 Kelvin (around -60°C). One aspect of this change is a difference in the period of the magnetic order. Unlike the ordering at low temperatures, the magnetic structure in the temperature range 213 K to 230 K is incommensurate: its period does not ‘fit’ with the period of the crystal structure of copper and oxygen atoms. To be precise, a full rotation of the direction of the magnetic moment does not require exactly four atomic separations, but a little more or a little less, depending on the direction. (Credit: Image courtesy of Paul Scherrer Institut (PSI))

ScienceDaily (Jan. 23, 2012) — In first-of-their-kind experiments performed at the American X-ray laser LCLS, a collaboration led by researchers from the Paul Scherrer Institute has been able to precisely follow how the magnetic structure of a material changes.

This is another milestone, because such investigations will also be a major focus of research at the planned Swiss X-ray Laser, Swiss FEL, at PSI. The results could contribute to the development of new technologies for magnetic storage media for the future.The study was carried out on cupric oxide (CuO). The change of structure was initiated by a laser pulse, and then, with the help of short X-ray pulses, near-instantaneous images were obtained at different points in time for individual intermediate steps during the process. It appears as if the structure begins to change 400 femtoseconds after the laser pulse strikes (1 femtosecond = 0.000 000 000 000 001 seconds). Apparently, the fundamental magnets within the material need that much time to communicate with each other and then react. In addition to this scientific result, the work proves that it is actually possible with X-ray lasers to follow certain types of extremely rapid magnetic processes.

The researchers have reported on their work in the latest edition of the technical journal Physical Review Letters (PRL).

Materials with particular magnetic properties are the basis of many current technologies, in particular, data storage on hard discs and in other media. For this, the magnetic orientation in the material is most often used: the atoms in the material behave to some extent like tiny rod magnets ("spins"). These mini-magnets can be oriented in different ways and information can be stored through their orientation. For efficient data storage, it is crucial that old data can be rapidly overwritten. This is possible if the magnetic orientation in a material can be altered in a very short time. To develop innovative materials which can store data quickly, it is therefore important to understand exactly how this change occurs as a function of time.

Magnetic orientation in motion

In experiments performed at the X-ray laser LCLS at Stanford, California, a collaboration led by researchers from the Paul Scherrer Institute have been able to study the magnetic orientation in cupric oxide, CuO. This material demonstrates completely different magnetic orientations depending on temperature: Below -60°C, the spins, which function in the copper atoms (Cu) like magnets, point periodically in one direction and then the opposite; between -60°C and -43°C, they are arranged helically, as if they were forming a spiral staircase. Although the spin orientations for the two arrangements have been known for some time, the time required to move from one arrangement to the other has only now been shown by the experiment.

"In our investigation, we began with a 'cold' sample and then heated it with an intense flash of light from an optical laser," explains Steven Johnson, spokesman for the PSI experiment. "Shortly after this, we determined the structure of the sample by illuminating it with an extremely short pulse from an X-ray laser. When we repeated this at different time intervals between the flash of light and the X-ray pulse, we were able to reconstruct the course of the change in the magnetic structure."

Mini-magnets need 400 femtoseconds to agree amongst themselves.

The results show that it takes about 400 femtoseconds before the magnetic structure begins to alter visibly. Then the structure gradually reaches its final state. The more intense the initiating flash of light, the faster the change of state. "The spins of all copper atoms are involved in the magnetic structure. Thus the atoms at opposite ends of the material must be coordinated before the structure can change. This takes 400 femtoseconds," explains Urs Staub, one of the PSI researchers responsible. "For cupric oxide, that is the fundamental limit; it simply cannot happen faster than that. This depends upon how strongly the spins are coupled between neighbouring atoms."

There is a good reason why the researchers were particularly interested in cupric oxide. Along with the screw-like magnetic orientation that occurs between -60°C and -43°C, the material is also 'multiferroic', a material where electrical and magnetic processes mutually influence one another. These materials have many different potential areas of application where magnetism and electronics interact.

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The above story is reprinted from materials provided byPaul Scherrer Institut (PSI), via AlphaGalileo.

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Journal Reference:

1. S. Johnson, R. de Souza, U. Staub, P. Beaud, E. Möhr-Vorobeva, G. Ingold, A. Caviezel, V. Scagnoli, W. Schlotter, J. Turner, O. Krupin, W.-S. Lee, Y.-D. Chuang, L. Patthey, R. Moore, D. Lu, M. Yi, P. Kirchmann, M. Trigo, P. Denes, D. Doering, Z. Hussain, Z.-X. Shen, D. Prabhakaran, A. Boothroyd. Femtosecond Dynamics of the Collinear-to-Spiral Antiferromagnetic Phase Transition in CuO.Physical Review Letters, 2012; 108 (3) DOI:10.1103/PhysRevLett.108.037203

Cooling Semiconductors by Laser Light

The experiments are carried out in the Quantop laboratories at the Niels Bohr Institute. The laser light that hits the semiconducting nanomembrane is controlled with a forest of mirrors. (Credit: Ola J. Joensen)

ScienceDaily (Jan. 22, 2012) — Researchers at the Niels Bohr Institute have combined two fields -- quantum physics and nano physics -- and this has led to the discovery of a new method for laser cooling semiconductor membranes. Semiconductors are vital components in solar cells, LEDs and many other electronics, and the efficient cooling of components is important for future quantum computers and ultrasensitive sensors. The new cooling method works quite paradoxically by heating the material! Using lasers, researchers cooled membrane fluctuations to minus 269 degrees C.

The results are published in the journal Nature Physics.

"In experiments, we have succeeded in achieving a new and efficient cooling of a solid material by using lasers. We have produced a semiconductor membrane with a thickness of 160 nanometers and an unprecedented surface area of 1 by 1 millimeter. In the experiments, we let the membrane interact with the laser light in such a way that its mechanical movements affected the light that hit it. We carefully examined the physics and discovered that a certain oscillation mode of the membrane cooled from room temperature down to minus 269 degrees C, which was a result of the complex and fascinating interplay between the movement of the membrane, the properties of the semiconductor and the optical resonances," explains Koji Usami, associate professor at Quantop at the Niels Bohr Institute.

From gas to solid

Laser cooling of atoms has been practiced for several years in experiments in the quantum optical laboratories of the Quantop research group at the Niels Bohr Institute. Here researchers have cooled gas clouds of cesium atoms down to near absolute zero, minus 273 degrees C, using focused lasers and have created entanglement between two atomic systems. The atomic spin becomes entangled and the two gas clouds have a kind of link, which is due to quantum mechanics. Using quantum optical techniques, they have measured the quantum fluctuations of the atomic spin.

"For some time we have wanted to examine how far you can extend the limits of quantum mechanics -- does it also apply to macroscopic materials? It would mean entirely new possibilities for what is called optomechanics, which is the interaction between optical radiation, i.e. light, and a mechanical motion," explains Professor Eugene Polzik, head of the Center of Excellence Quantop at the Niels Bohr Institute at the University of Copenhagen.

But they had to find the right material to work with.

Lucky coincidence

In 2009, Peter Lodahl (who is today a professor and head of the Quantum Photonic research group at the Niels Bohr Institute) gave a lecture at the Niels Bohr Institute, where he showed a special photonic crystal membrane that was made of the semiconducting material gallium arsenide (GaAs). Eugene Polzik immediately thought that this nanomembrane had many advantageous electronic and optical properties and he suggested to Peter Lodahl's group that they use this kind of membrane for experiments with optomechanics. But this required quite specific dimensions and after a year of trying they managed to make a suitable one.

"We managed to produce a nanomembrane that is only 160 nanometers thick and with an area of more than 1 square millimetre. The size is enormous, which no one thought it was possible to produce," explains Assistant Professor Søren Stobbe, who also works at the Niels Bohr Institute.

Basis for new research

Now a foundation had been created for being able to reconcile quantum mechanics with macroscopic materials to explore the optomechanical effects.

Koji Usami explains that in the experiment they shine the laser light onto the nanomembrane in a vacuum chamber. When the laser light hits the semiconductor membrane, some of the light is reflected and the light is reflected back again via a mirror in the experiment so that the light flies back and forth in this space and forms an optical resonator. Some of the light is absorbed by the membrane and releases free electrons. The electrons decay and thereby heat the membrane and this gives a thermal expansion. In this way the distance between the membrane and the mirror is constantly changed in the form of a fluctuation.

"Changing the distance between the membrane and the mirror leads to a complex and fascinating interplay between the movement of the membrane, the properties of the semiconductor and the optical resonances and you can control the system so as to cool the temperature of the membrane fluctuations. This is a new optomechanical mechanism, which is central to the new discovery. The paradox is that even though the membrane as a whole is getting a little bit warmer, the membrane is cooled at a certain oscillation and the cooling can be controlled with laser light. So it is cooling by warming! We managed to cool the membrane fluctuations to minus 269 degrees C," Koji Usami explains.

"The potential of optomechanics could, for example, pave the way for cooling components in quantum computers. Efficient cooling of mechanical fluctuations of semiconducting nanomembranes by means of light could also lead to the development of new sensors for electric current and mechanical forces. Such cooling in some cases could replace expensive cryogenic cooling, which is used today and could result in extremely sensitive sensors that are only limited by quantum fluctuations," says Professor Eugene Polzik.

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Journal Reference:

1. K. Usami, A. Naesby, T. Bagci, B. Melholt Nielsen, J. Liu, S. Stobbe, P. Lodahl, E. S. Polzik. Optical cavity cooling of mechanical modes of a semiconductor nanomembrane. Nature Physics, 2012;

Laser light used to cool object to quantum ground state

ScienceDaily (Oct. 9, 2011) — For the first time, researchers at the California Institute of Technology (Caltech), in collaboration with a team from the University of Vienna, have managed to cool a miniature mechanical object to its lowest possible energy state using laser light. The achievement paves the way for the development of exquisitely sensitive detectors as well as for quantum experiments that scientists have long dreamed of conducting.

"We've taken a solid mechanical system -- one made up of billions of atoms -- and used optical light to put it into a state in which it behaves according to the laws of quantum mechanics. In the past, this has only been achieved with trapped single atoms or ions," says Oskar Painter, professor of applied physics and executive officer for applied physics and materials science at Caltech and the principal investigator on a paper describing the work that appears in the October 6 issue of the journal Nature.

As described in the paper, Painter and his colleagues have engineered a nanoscale object -- a tiny mechanical silicon beam -- such that laser light of a carefully selected frequency can enter the system and, once reflected, can carry thermal energy away, cooling the system.

By carefully designing each element of the beam as well as a patterned silicon shield that isolates it from the environment, Painter and colleagues were able to use the laser cooling technique to bring the system down to the quantum ground state, where mechanical vibrations are at an absolute minimum. Such a cold mechanical object could help detect very small forces or masses, whose presence would normally be masked by the noisy thermal vibrations of the sensor.

"In many ways, the experiment we've done provides a starting point for the really interesting quantum-mechanical experiments one wants to do," Painter says. For example, scientists would like to show that a mechanical system could be coaxed into a quantum superposition -- a bizarre quantum state in which a physical system can exist in more than one position at once. But they need a system at the quantum ground state to begin such experiments.

To reach the ground state, Painter's group had to cool its mechanical beam to a temperature below 100 millikelvin (-273.15°C). That's because the beam is designed to vibrate at gigahertz frequencies (corresponding to a billion cycles per second) -- a range where a large number of phonons are present at room temperature. Phonons are the most basic units of vibration just as the most basic units or packets of light are called photons. All of the phonons in a system have to be removed to cool it to the ground state.

Conventional means of cryogenically cooling to such temperatures exist but require expensive and, in some cases, impractical equipment. There's also the problem of figuring out how to measure such a cold mechanical system. To solve both problems, the Caltech team used a different cooling strategy.

"What we've done is used the photons -- the light field -- to extract phonons from the system," says Jasper Chan, lead author of the new paper and a graduate student in Painter's group. To do so, the researchers drilled tiny holes at precise locations in their mechanical beam so that when they directed laser light of a particular frequency down the length of the beam, the holes acted as mirrors, trapping the light in a cavity and causing it to interact strongly with the mechanical vibrations of the beam.

Because a shift in the frequency of the light is directly related to the thermal motion of the mechanical object, the light -- when it eventually escapes from the cavity -- also carries with it information about the mechanical system, such as the motion and temperature of the beam. Thus, the researchers have created an efficient optical interface to a mechanical element -- or an optomechanical transducer -- that can convert information from the mechanical system into photons of light.

Importantly, since optical light, unlike microwaves or electrons, can be transmitted over large, kilometer-length distances without attenuation, such an optomechanical transducer could be useful for linking different quantum systems -- a microwave system with an optical system, for example. While Painter's system involves an optical interface to a mechanical element, other teams have been developing systems that link a microwave interface to a mechanical element. What if those two mechanical elements were the same? "Then," says Painter, "I could imagine connecting the microwave world to the optical world via this mechanical conduit one photon at a time."

The Caltech team isn't the first to cool a nanomechanical object to the quantum ground state; a group led by former Caltech postdoctoral scholar Andrew Cleland, now at the University of California, Santa Barbara, accomplished this in 2010 using more conventional refrigeration techniques, and, earlier this year, a group from the National Institute of Standards and Technology in Boulder, Colorado, cooled an object to the ground state using microwave radiation. The new work, however, is the first in which a nanomechanical object has been put into the ground state using optical light.

"This is an exciting development because there are so many established techniques for manipulating and measuring the quantum properties of systems using optics," Painter says.

The other cooling techniques used starting temperatures of approximately 20 millikelvin -- more than a factor of 10,000 times cooler than room temperature. Ideally, to simplify designs, scientists would like to initiate these experiments at room temperature. Using laser cooling, Painter and his colleagues were able to perform their experiment at a much higher temperature -- only about 10 times lower than room temperature.

The work was supported by Caltech's Kavli Nanoscience Institute; the Defense Advanced Research Projects Agency's Microsystems Technology Office through a grant from the Air Force Office of Scientific Research; the European Commission; the European Research Council; and the Austrian Science Fund.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by California Institute of Technology, via EurekAlert!, a service of AAAS.

Journal Reference:

Jasper Chan, T. P. Mayer Alegre, Amir H. Safavi-Naeini, Jeff T. Hill, Alex Krause, Simon Gröblacher, Markus Aspelmeyer, Oskar Painter. Laser cooling of a nanomechanical oscillator into its quantum ground state. Nature, 2011; 478 (7367): 89 DOI: 10.1038/nature10461

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High-quality white light produced by four-color laser source; Diode lasers could challenge LEDs for home and industrial lighting supremacy

ScienceDaily (Oct. 26, 2011) — The human eye is as comfortable with white light generated by diode lasers as with that produced by increasingly popular light-emitting diodes (LEDs), according to tests conceived at Sandia National Laboratories.

Both technologies pass electrical current through material to generate light, but the simpler LED emits lights only through spontaneous emission. Diode lasers bounce light back and forth internally before releasing it.

The finding is important because LEDs -- widely accepted as more efficient and hardier replacements for century-old tungsten incandescent bulb technology -- lose efficiency at electrical currents above 0.5 amps. However, the efficiency of a sister technology -- the diode laser -- improves at higher currents, providing even more light than LEDs at higher amperages.

"What we showed is that diode lasers are a worthy path to pursue for lighting," said Sandia researcher Jeff Tsao, who proposed the comparative experiment. "Before these tests, our research in this direction was stopped before it could get started. The typical response was, 'Are you kidding? The color rendering quality of white light produced by diode lasers would be terrible.' So finally it seemed like, in order to go further, one really had to answer this very basic question first."

Little research had been done on diode lasers for lighting because of a widespread assumption that human eyes would find laser-based white light unpleasant. It would comprise four extremely narrow-band wavelengths -- blue, red, green, and yellow -- and would be very different from sunlight, for example, which blends a wide spectrum of wavelengths with no gaps in between. Diode laser light is also ten times narrower than that emitted by LEDs.

The tests -- a kind of high-tech market research -- took place at the University of New Mexico's Center for High Technology Materials. Forty volunteers were seated, one by one, before two near-identical scenes of fruit in bowls, housed in adjacent chambers. Each bowl was randomly illuminated by warm, cool, or neutral white LEDs, by a tungsten-filament incandescent light bulb, or by a combination of four lasers (blue, red, green, yellow) tuned so their combination produced a white light.

The experiment proceeded like an optometrist's exam: the subjects were asked: Do you prefer the left picture, or the right? All right, how about now?

The viewers were not told which source provided the illumination. They were instructed merely to choose the lit scene with which they felt most comfortable. The pairs were presented in random order to ensure that neither sequence nor tester preconceptions played roles in subject choices, but only the lighting itself. The computer program was written, and the set created, by Alexander Neumann, a UNM doctoral student of CHTM director Steve Brueck.

Each participant, selected from a variety of age groups, was asked to choose 80 times between the two changing alternatives, a procedure that took ten to twenty minutes, said Sandia scientist Jonathan Wierer, who helped plan, calibrate and execute the experiments. Five results were excluded when the participants proved to be color-blind. The result was that there was a statistically significant preference for the diode-laser-based white light over the warm and cool LED-based white light, Wierer said, but no statistically significant preference between the diode-laser-based and either the neutral LED-based or incandescent white light.

The results probably won't start a California gold rush of lighting fabricators into diode lasers, said Tsao, but they may open a formerly ignored line of research. Diode lasers are slightly more expensive to fabricate than LEDs because their substrates must have fewer defects than those used for LEDs. Still, he said, such substrates are likely to become more available in the future because they improve LED performance as well.

Also, while blue diode lasers have good enough performance that the automaker BMW is planning their use in its vehicles' next-generation white headlights, performance of red diode lasers is not as good, and yellow and green have a ways to go before they are efficient enough for commercial lighting opportunities.

Still, says Tsao, a competition wouldn't have to be all or nothing. Instead, he said, a cooperative approach might use blue and red diode lasers with yellow and green LEDs. Or blue diode lasers could be used to illuminate phosphors -- the technique currently used by fluorescent lights and the current generation of LED-based white light -- to create desirable shades of light.

The result makes possible still further efficiencies for the multibillion dollar lighting industry. The so-called ''smart beams'' can be adjusted on site for personalized color renderings for health reasons and, because they are directional, also can provide illumination precisely where it's wanted.

Colorimetric and experimental guidance was provided by the National Institute of Standards and Technology.

The research was published in the July 1 issue of Optics Express.

This work was conducted as part of the Solid-State Lighting Science Energy Frontier Research Center, funded by the U.S. DOE Office of Science.

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Journal Reference:

A. Neumann, J. J. Wierer, W. Davis, Y. Ohno, S. R. J. Brueck, J.Y. Tsao. Four-color laser white illuminant demonstrating high color-rendering quality. Optics Express, 2011; 19 (S4): A982 DOI: 10.1364/OE.19.00A982

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Laser ion source will produce a new generation of semiconductors

ScienceDaily (Oct. 20, 2011) — For ion implantation, that is 'hammering' ions into the surface layer of the material, conventional ion accelerators are commonly used. Laser ion sources are much simpler, cheaper and more universal. However, they emit wide energy ions usually accompanied by some admixtures. In the Institute of Plasma Physics and Laser Microfusion in Warsaw a unique laser ion source has been built which is equipped with a special system for accelerating ions to a chosen energy and for eliminating admixtures. This device has already been used to produce samples of a new generation of semiconductors: a layer of silica (SiO2) in which germanium nanocrystals have been formed.

Laser Ion Sources (LIS) are simple devices that produce ions in interaction of a focused laser beam with the target placed in a vacuum vessel. Admixtures that happen to be in the target often cause problems -- together with the proper ions, they can modify the sample. Moreover, the laser pulse also pulls out atoms and debris from the target which are deposited on the irradiated sample and modify its surface. "To prevent such effects, we have designed and built a device for ion implantation with a unique electric system for ion acceleration," says Marcin Rosinski, a PhD student from the Institute of Plasma Physics and Laser Microfusion (IPPLM) in Warsaw.

Ion implementation is the process of embedding ions into the surface layer of the sample in order to change some properties of the material, mechanical or electrical. Currently, ion accelerators are routinely used for this purpose. Laser ion sources have a chance to excel those devices: they are smaller, simpler and can produce ions from high-melting materials such as tantalum or tungsten. What is more, the ion beam can easily be modified by the change of parameters and the geometry of the laser-target-sample system. The released ions can well be accelerated in the external electric field.

However, to be able to use the LIS type sources in industry, some requirements must be fulfilled: the beam of ions cannot possess impurities and the ions should have almost the same specific energy. To meet both requirements the laser ion source with special electrostatic system must be applied.

In the device built at the IPPLM the low-energy laser pulse lasts 3.5 nanoseconds. The laser pulse energy, in the first phase of laser-matter interaction, is transferred to free electrons which subsequently ionise atoms of target material and admixtures. The main part of the laser pulse energy directly heats ionised matter (plasma) causing its quick expansion. A broad energy distribution of the ions expanding from plasma results from the nature of the process of plasma generation.

Some particles and debris extracted from the target by the laser pulse are electrically neutral, which is why they expand without deflection in the electric field and go straight onto the screen that is placed exactly on the axis of the system, to shield the sample. At the same time, laser-produced ions which avoid the screen are accelerated and focused by the electric field on the sample located on the axis behind the screen. "We have selected the parameters of the field in such a way that only the chosen ions of the target reach the sample. The spot of the focused beam is 1 mm in diameter," explains Rosinski.

The low-energy laser used in the experiment does not heat itself and is capable of generating 10 thousand or more laser pulses within some ten minutes. Those advantages make it possible for scientists to control precisely the number of ions that reach the sample.

The solution proposed by the scientists from the IPPLM has successfully been used to explore the process of germanium ion implantation in silica (SiO2) layer with a view to fabricate germanium nanocrystals within it. Thus, a modified semiconductor has been created whose prospective implementation in electronics is widely anticipated, for example in miniaturisation of some memory chips or in elements for light emission.

To obtain germanium nanocrystals from the laser-produced ions, the implanted sample should be heated in the temperature of 600 to 1200 Celsius degrees. In this process some germanium crystals, ranging in size from a few to 20 nanometres (billionth of a metre) are created. "Our implanted samples, after heating, are examined with the use of various sophisticated, currently available measuring methods in the specialised laboratories, mainly at the Universities in Messina and Catania in Sicily. We have analysed both the results of ion implantation and the formation of nanocrystal structures in the samples," says Rosinski.

Laser ion source built and tested at the IPPLM is a prototype device expected to find applications in industry. "In two years, we will have finished the work connected with optimization of our device regarding industrial usage but we have already started looking for enterprises that are interested in implementing this technology," summarises Prof. Jerzy Wolowski, the Head of Laser Plasma Division at the IPPLM.

The construction of the device for laser induced implantation was started at the IPPLM a few years ago within the framework of European SEMINANO project.

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Laser light used to cool object to quantum ground state

ScienceDaily (Oct. 9, 2011) — For the first time, researchers at the California Institute of Technology (Caltech), in collaboration with a team from the University of Vienna, have managed to cool a miniature mechanical object to its lowest possible energy state using laser light. The achievement paves the way for the development of exquisitely sensitive detectors as well as for quantum experiments that scientists have long dreamed of conducting.

"We've taken a solid mechanical system -- one made up of billions of atoms -- and used optical light to put it into a state in which it behaves according to the laws of quantum mechanics. In the past, this has only been achieved with trapped single atoms or ions," says Oskar Painter, professor of applied physics and executive officer for applied physics and materials science at Caltech and the principal investigator on a paper describing the work that appears in the October 6 issue of the journal Nature.

As described in the paper, Painter and his colleagues have engineered a nanoscale object -- a tiny mechanical silicon beam -- such that laser light of a carefully selected frequency can enter the system and, once reflected, can carry thermal energy away, cooling the system.

By carefully designing each element of the beam as well as a patterned silicon shield that isolates it from the environment, Painter and colleagues were able to use the laser cooling technique to bring the system down to the quantum ground state, where mechanical vibrations are at an absolute minimum. Such a cold mechanical object could help detect very small forces or masses, whose presence would normally be masked by the noisy thermal vibrations of the sensor.

"In many ways, the experiment we've done provides a starting point for the really interesting quantum-mechanical experiments one wants to do," Painter says. For example, scientists would like to show that a mechanical system could be coaxed into a quantum superposition -- a bizarre quantum state in which a physical system can exist in more than one position at once. But they need a system at the quantum ground state to begin such experiments.

To reach the ground state, Painter's group had to cool its mechanical beam to a temperature below 100 millikelvin (-273.15°C). That's because the beam is designed to vibrate at gigahertz frequencies (corresponding to a billion cycles per second) -- a range where a large number of phonons are present at room temperature. Phonons are the most basic units of vibration just as the most basic units or packets of light are called photons. All of the phonons in a system have to be removed to cool it to the ground state.

Conventional means of cryogenically cooling to such temperatures exist but require expensive and, in some cases, impractical equipment. There's also the problem of figuring out how to measure such a cold mechanical system. To solve both problems, the Caltech team used a different cooling strategy.

"What we've done is used the photons -- the light field -- to extract phonons from the system," says Jasper Chan, lead author of the new paper and a graduate student in Painter's group. To do so, the researchers drilled tiny holes at precise locations in their mechanical beam so that when they directed laser light of a particular frequency down the length of the beam, the holes acted as mirrors, trapping the light in a cavity and causing it to interact strongly with the mechanical vibrations of the beam.

Because a shift in the frequency of the light is directly related to the thermal motion of the mechanical object, the light -- when it eventually escapes from the cavity -- also carries with it information about the mechanical system, such as the motion and temperature of the beam. Thus, the researchers have created an efficient optical interface to a mechanical element -- or an optomechanical transducer -- that can convert information from the mechanical system into photons of light.

Importantly, since optical light, unlike microwaves or electrons, can be transmitted over large, kilometer-length distances without attenuation, such an optomechanical transducer could be useful for linking different quantum systems -- a microwave system with an optical system, for example. While Painter's system involves an optical interface to a mechanical element, other teams have been developing systems that link a microwave interface to a mechanical element. What if those two mechanical elements were the same? "Then," says Painter, "I could imagine connecting the microwave world to the optical world via this mechanical conduit one photon at a time."

The Caltech team isn't the first to cool a nanomechanical object to the quantum ground state; a group led by former Caltech postdoctoral scholar Andrew Cleland, now at the University of California, Santa Barbara, accomplished this in 2010 using more conventional refrigeration techniques, and, earlier this year, a group from the National Institute of Standards and Technology in Boulder, Colorado, cooled an object to the ground state using microwave radiation. The new work, however, is the first in which a nanomechanical object has been put into the ground state using optical light.

"This is an exciting development because there are so many established techniques for manipulating and measuring the quantum properties of systems using optics," Painter says.

The other cooling techniques used starting temperatures of approximately 20 millikelvin -- more than a factor of 10,000 times cooler than room temperature. Ideally, to simplify designs, scientists would like to initiate these experiments at room temperature. Using laser cooling, Painter and his colleagues were able to perform their experiment at a much higher temperature -- only about 10 times lower than room temperature.

The work was supported by Caltech's Kavli Nanoscience Institute; the Defense Advanced Research Projects Agency's Microsystems Technology Office through a grant from the Air Force Office of Scientific Research; the European Commission; the European Research Council; and the Austrian Science Fund.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by California Institute of Technology, via EurekAlert!, a service of AAAS.

Journal Reference:

Jasper Chan, T. P. Mayer Alegre, Amir H. Safavi-Naeini, Jeff T. Hill, Alex Krause, Simon Gröblacher, Markus Aspelmeyer, Oskar Painter. Laser cooling of a nanomechanical oscillator into its quantum ground state. Nature, 2011; 478 (7367): 89 DOI: 10.1038/nature10461

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Laser ion source will produce a new generation of semiconductors

ScienceDaily (Oct. 20, 2011) — For ion implantation, that is 'hammering' ions into the surface layer of the material, conventional ion accelerators are commonly used. Laser ion sources are much simpler, cheaper and more universal. However, they emit wide energy ions usually accompanied by some admixtures. In the Institute of Plasma Physics and Laser Microfusion in Warsaw a unique laser ion source has been built which is equipped with a special system for accelerating ions to a chosen energy and for eliminating admixtures. This device has already been used to produce samples of a new generation of semiconductors: a layer of silica (SiO2) in which germanium nanocrystals have been formed.

Laser Ion Sources (LIS) are simple devices that produce ions in interaction of a focused laser beam with the target placed in a vacuum vessel. Admixtures that happen to be in the target often cause problems -- together with the proper ions, they can modify the sample. Moreover, the laser pulse also pulls out atoms and debris from the target which are deposited on the irradiated sample and modify its surface. "To prevent such effects, we have designed and built a device for ion implantation with a unique electric system for ion acceleration," says Marcin Rosinski, a PhD student from the Institute of Plasma Physics and Laser Microfusion (IPPLM) in Warsaw.

Ion implementation is the process of embedding ions into the surface layer of the sample in order to change some properties of the material, mechanical or electrical. Currently, ion accelerators are routinely used for this purpose. Laser ion sources have a chance to excel those devices: they are smaller, simpler and can produce ions from high-melting materials such as tantalum or tungsten. What is more, the ion beam can easily be modified by the change of parameters and the geometry of the laser-target-sample system. The released ions can well be accelerated in the external electric field.

However, to be able to use the LIS type sources in industry, some requirements must be fulfilled: the beam of ions cannot possess impurities and the ions should have almost the same specific energy. To meet both requirements the laser ion source with special electrostatic system must be applied.

In the device built at the IPPLM the low-energy laser pulse lasts 3.5 nanoseconds. The laser pulse energy, in the first phase of laser-matter interaction, is transferred to free electrons which subsequently ionise atoms of target material and admixtures. The main part of the laser pulse energy directly heats ionised matter (plasma) causing its quick expansion. A broad energy distribution of the ions expanding from plasma results from the nature of the process of plasma generation.

Some particles and debris extracted from the target by the laser pulse are electrically neutral, which is why they expand without deflection in the electric field and go straight onto the screen that is placed exactly on the axis of the system, to shield the sample. At the same time, laser-produced ions which avoid the screen are accelerated and focused by the electric field on the sample located on the axis behind the screen. "We have selected the parameters of the field in such a way that only the chosen ions of the target reach the sample. The spot of the focused beam is 1 mm in diameter," explains Rosinski.

The low-energy laser used in the experiment does not heat itself and is capable of generating 10 thousand or more laser pulses within some ten minutes. Those advantages make it possible for scientists to control precisely the number of ions that reach the sample.

The solution proposed by the scientists from the IPPLM has successfully been used to explore the process of germanium ion implantation in silica (SiO2) layer with a view to fabricate germanium nanocrystals within it. Thus, a modified semiconductor has been created whose prospective implementation in electronics is widely anticipated, for example in miniaturisation of some memory chips or in elements for light emission.

To obtain germanium nanocrystals from the laser-produced ions, the implanted sample should be heated in the temperature of 600 to 1200 Celsius degrees. In this process some germanium crystals, ranging in size from a few to 20 nanometres (billionth of a metre) are created. "Our implanted samples, after heating, are examined with the use of various sophisticated, currently available measuring methods in the specialised laboratories, mainly at the Universities in Messina and Catania in Sicily. We have analysed both the results of ion implantation and the formation of nanocrystal structures in the samples," says Rosinski.

Laser ion source built and tested at the IPPLM is a prototype device expected to find applications in industry. "In two years, we will have finished the work connected with optimization of our device regarding industrial usage but we have already started looking for enterprises that are interested in implementing this technology," summarises Prof. Jerzy Wolowski, the Head of Laser Plasma Division at the IPPLM.

The construction of the device for laser induced implantation was started at the IPPLM a few years ago within the framework of European SEMINANO project.

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NASA to demonstrate communications via laser beam

ScienceDaily (Sep. 24, 2011) — It currently takes 90 minutes to transmit high-resolution images from Mars, but NASA would like to dramatically reduce that time to just minutes. A new optical communications system that NASA plans to demonstrate in 2016 will lead the way and even allow the streaming of high-definition video from distances beyond the Moon.

This dramatically enhanced transmission speed will be demonstrated by the Laser Communications Relay Demonstration (LCRD), one of three projects selected by NASA's Office of the Chief Technologist (OCT) for a trial run. To be developed by a team led by engineers at the NASA Goddard Space Flight Center in Greenbelt, Md., LCRD is expected to fly as a hosted payload on a commercial communications satellite developed by Space Systems/Loral, of Palo Alto, Calif.

"We want to take NASA's communications capabilities to the next level," said LCRD Principal Investigator Dave Israel, who is leading a multi-organizational team that includes NASA's Jet Propulsion Laboratory, Pasadena, Calif. and Lincoln Laboratory at the Massachusetts Institute of Technology, Cambridge, Mass. Although NASA has developed higher data-rate radio frequency systems, data-compression, and other techniques to boost the amount of data that its current systems can handle, the Agency's capabilities will not keep pace with the projected data needs of advanced instruments and future human exploration, Israel added.

"Just as the home Internet user hit the wall with dial-up, NASA is approaching the limit of what its existing communications network can handle," he said.

The solution is to augment NASA's legacy radio-based network, which includes a fleet of tracking and data relay satellites and a network of ground stations, with optical systems, which could increase data rates by anywhere from 10 to 100 times. "This transition will take several years to complete, but the eventual payback will be very large increases in the amount of data we can transmit, both downlink and uplink, especially to distant destinations in the solar system and beyond," said James Reuther, director of OCT's Crosscutting Technology Demonstrations Division.

First Step

The LCRD is the next step in that direction, Israel said, likening the emerging capability to land-based fiber-optic systems, such as Verizon's FiOS network. "In a sense, we're moving FiOS to space."

To demonstrate the new capability, the Goddard team will encode digital data and transmit the information via laser light from specially equipped ground stations to an experimental payload hosted on the commercial communications satellite.

The payload will include telescopes, lasers, mirrors, detectors, a pointing and tracking system, control electronics, and two different types of modems. One modem is ideal for communicating with deep space missions or tiny, low-power smallsats operating in low-Earth orbit. The other can handle much higher data rates, particularly from Earth-orbiting spacecraft, including the International Space Station. "With the higher-speed modem type, future systems could support data rates of tens of gigabits per second," Israel said.

Once the payload receives the data, it would then relay it back to ground stations now scheduled to operate in Hawaii and Southern California.

The multiple ground stations are important to demonstrating a fully operational system, Israel said. Cloud cover and turbulent atmospheric conditions impede laser communications, requiring a clear line of sight between the transmitter and receiver. If bad weather prevents a signal from being sent or received at one location, the network could hand over the responsibility to one of the other ground stations or store it for later retransmission.

The demonstration is expected to run two to three years.

Follow-On to LADEE Experiment

The project isn't NASA's first foray into laser communications. Goddard engineers are now developing a laser communications payload for NASA's Lunar Atmosphere and Dust Environment Explorer (LADEE), which the Agency plans to launch in 2013 to characterize the Moon's wisp-thin atmosphere and dust environment. The main goal of the LADEE experiment is proving fundamental concepts of laser-based communications and transferring up to 622 megabits per second, which is about five times the current state-of-the-art from lunar distances.

However, the LADEE payload, called the Lunar Laser Communications Demonstration (LLCD), is equipped with only one modem, the lower-speed model best suited for deep space communications. In addition, LADEE is a short-duration mission. LLCD is expected to operate for only 16 days of the LADEE mission, not enough time to demonstrate a fully operational laser-communications network, Israel said.

"What we're trying to do is get ahead of the curve," Israel said. "We want to get to the point where communications is no longer a constraint on scientists who want to gather more data, but are worried about getting their data back from space."

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NASA to demonstrate communications via laser beam

ScienceDaily (Sep. 24, 2011) — It currently takes 90 minutes to transmit high-resolution images from Mars, but NASA would like to dramatically reduce that time to just minutes. A new optical communications system that NASA plans to demonstrate in 2016 will lead the way and even allow the streaming of high-definition video from distances beyond the Moon.

This dramatically enhanced transmission speed will be demonstrated by the Laser Communications Relay Demonstration (LCRD), one of three projects selected by NASA's Office of the Chief Technologist (OCT) for a trial run. To be developed by a team led by engineers at the NASA Goddard Space Flight Center in Greenbelt, Md., LCRD is expected to fly as a hosted payload on a commercial communications satellite developed by Space Systems/Loral, of Palo Alto, Calif.

"We want to take NASA's communications capabilities to the next level," said LCRD Principal Investigator Dave Israel, who is leading a multi-organizational team that includes NASA's Jet Propulsion Laboratory, Pasadena, Calif. and Lincoln Laboratory at the Massachusetts Institute of Technology, Cambridge, Mass. Although NASA has developed higher data-rate radio frequency systems, data-compression, and other techniques to boost the amount of data that its current systems can handle, the Agency's capabilities will not keep pace with the projected data needs of advanced instruments and future human exploration, Israel added.

"Just as the home Internet user hit the wall with dial-up, NASA is approaching the limit of what its existing communications network can handle," he said.

The solution is to augment NASA's legacy radio-based network, which includes a fleet of tracking and data relay satellites and a network of ground stations, with optical systems, which could increase data rates by anywhere from 10 to 100 times. "This transition will take several years to complete, but the eventual payback will be very large increases in the amount of data we can transmit, both downlink and uplink, especially to distant destinations in the solar system and beyond," said James Reuther, director of OCT's Crosscutting Technology Demonstrations Division.

First Step

The LCRD is the next step in that direction, Israel said, likening the emerging capability to land-based fiber-optic systems, such as Verizon's FiOS network. "In a sense, we're moving FiOS to space."

To demonstrate the new capability, the Goddard team will encode digital data and transmit the information via laser light from specially equipped ground stations to an experimental payload hosted on the commercial communications satellite.

The payload will include telescopes, lasers, mirrors, detectors, a pointing and tracking system, control electronics, and two different types of modems. One modem is ideal for communicating with deep space missions or tiny, low-power smallsats operating in low-Earth orbit. The other can handle much higher data rates, particularly from Earth-orbiting spacecraft, including the International Space Station. "With the higher-speed modem type, future systems could support data rates of tens of gigabits per second," Israel said.

Once the payload receives the data, it would then relay it back to ground stations now scheduled to operate in Hawaii and Southern California.

The multiple ground stations are important to demonstrating a fully operational system, Israel said. Cloud cover and turbulent atmospheric conditions impede laser communications, requiring a clear line of sight between the transmitter and receiver. If bad weather prevents a signal from being sent or received at one location, the network could hand over the responsibility to one of the other ground stations or store it for later retransmission.

The demonstration is expected to run two to three years.

Follow-On to LADEE Experiment

The project isn't NASA's first foray into laser communications. Goddard engineers are now developing a laser communications payload for NASA's Lunar Atmosphere and Dust Environment Explorer (LADEE), which the Agency plans to launch in 2013 to characterize the Moon's wisp-thin atmosphere and dust environment. The main goal of the LADEE experiment is proving fundamental concepts of laser-based communications and transferring up to 622 megabits per second, which is about five times the current state-of-the-art from lunar distances.

However, the LADEE payload, called the Lunar Laser Communications Demonstration (LLCD), is equipped with only one modem, the lower-speed model best suited for deep space communications. In addition, LADEE is a short-duration mission. LLCD is expected to operate for only 16 days of the LADEE mission, not enough time to demonstrate a fully operational laser-communications network, Israel said.

"What we're trying to do is get ahead of the curve," Israel said. "We want to get to the point where communications is no longer a constraint on scientists who want to gather more data, but are worried about getting their data back from space."

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Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

First X-ray lasing of SACLA: Next-generation facility up and running with powerful new X-ray laser

ScienceDaily (June 13, 2011) — RIKEN and the Japan Synchrotron Radiation Research Institute (JASRI) have successfully produced a first beam of X-ray laser light with a wavelength of 1.2 Angstroms. This light was created using SACLA, a cutting-edge X-ray Free Electron Laser (XFEL) facility unveiled by RIKEN in February 2011 in Harima, Japan. SACLA (SPring-8 Angstrom Compact free electron LAser) opens a window into the structure of atoms and molecules at a level of detail never seen before.

The use of ultra high-intensity X-ray free electron laser light to explore the miniature structure of matter, until recently inconceivable, is today transforming how we visualize the atomic world. By providing much shorter wavelengths and higher intensities than other lasers, XFEL enables researchers to directly observe and manipulate objects on an unrivalled scale, opening new research opportunities in fields ranging from medicine and drug discovery to nanotechnology.

One of only two facilities in the world to offer this novel light source, SACLA has the capacity to deliver radiation one billion times brighter and with pulses one thousand times shorter than other existing X-ray sources. In late March, the facility marked its first milestone with beam acceleration to 8GeV and spontaneous X-rays of 0.8 Angstroms.

Only three months later, SACLA has marked a second milestone. On June 7, SACLA successfully increased the density of the electron beam by several hundred times and guided it with a precision of several micrometers to produce a bright X-ray laser with a wavelength of only 1.2 Angstroms (a photo energy of 10 keV). This matches the record of 1.2 Angstroms set at the only other operational XFEL facility in the world, the Linac Coherent Light Source (LCLS) in the United States.

With experiments soon to commence and user operations at the facility to begin by the end of fiscal 2011, this new record offers a taste of things to come with SACLA's powerful beam, the world's most advanced X-ray free electron laser.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by RIKEN.

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Single GFP-expressing cell is basis of living laser device

ScienceDaily (June 13, 2011) — It sounds like something out of a comic book or a science fiction movie -- a living laser -- but that is exactly what two investigators at the Wellman Center for Photomedicine at Massachusetts General Hospital have developed. In a report that will appear in the journal Nature Photonics and is receiving advance online release, Wellman researchers Malte Gather, PhD, and Seok Hyun Yun, PhD, describe how a single cell genetically engineered to express green fluorescent protein (GFP) can be used to amplify the light particles called photons into nanosecond-long pulses of laser light.

"Since they were first developed some 50 years ago, lasers have used synthetic materials such as crystals, dyes and purified gases as optical gain media, within which photon pulses are amplified as they bounces back and forth between two mirrors," says Yun, corresponding author of the report. "Ours is the first report of a successful biological laser based on a single, living cell."

Adds Gather, a research fellow and the paper's lead author, "Part of the motivation of this project was basic scientific curiosity. In addition to realizing that biological substances had not played a major role in lasers, we wondered whether there was a fundamental reason why laser light, as far as we know, does not occur in nature or if we could find a way to achieve lasing in biological substances or living organisms."

The investigators chose GFP for their exploration of those questions because the protein -- originally found in a species of jellyfish -- can be induced to emit light without the application of additional enzymes. Its properties are well understood, and there are established techniques to genetically program many organisms to express GFP. To determine the protein's potential for generating laser light, the researcher first assembled a device consisting of an inch-long cylinder, with mirrors at each end, filled with a solution of GFP in water. After first confirming that the GFP solution could amplify input energy into brief pulses of laser light, the researchers estimated the concentration of GFP required to produce the laser effect.

Using that information, their next step was to develop a line of mammalian cells expressing GFP at the required levels. The cellular laser was assembled by placing a single GFP-expressing cell -- with a diameter of from 15 to 20 millionths of a meter -- in a microcavity consisting of two highly reflective mirrors spaced 20 millionths of a meter apart. Not only did the cell-based device produce pulses of laser light as in the GFP solution experiment, the researchers also found that the spherical shape of the cell itself acted as a lens, refocusing the light and inducing emission of laser light at lower energy levels than required for the solution-based device. The cells used in the device survived the lasing process and were able to continue producing hundreds of pulses of laser light.

"While the individual laser pulses last for only a few nanoseconds, they are bright enough to be readily detected and appear to carry very useful information that may give us new ways to analyze the properties of large numbers of cells almost instantaneously," says Yun, who is an associate professor of Dermatology at Harvard Medical School. "And the ability to generate laser light from a biocompatible source placed inside a patient could be useful for photodynamic therapies, in which drugs are activated by the application of light, or novel forms of imaging."

Gather adds, "One of our long-term goals will be finding ways to bring optical communications and computing, currently done with inanimate electronic devices, into the realm of biotechnology. That could be particularly useful in projects requiring the interfacing of electronics with biological organisms. We also hope to be able to implant a structure equivalent to the mirrored chamber right into a cell, which would the next milestone in this research." The study was supported by grants from the National Science Foundation and the Korea National Research Foundation.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Massachusetts General Hospital, via EurekAlert!, a service of AAAS.

Journal Reference:

Malte C. Gather, Seok Hyun Yun. Single-cell biological lasers. Nature Photonics, 2011; DOI: 10.1038/nphoton.2011.99

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First X-ray lasing of SACLA: Next-generation facility up and running with powerful new X-ray laser

ScienceDaily (June 13, 2011) — RIKEN and the Japan Synchrotron Radiation Research Institute (JASRI) have successfully produced a first beam of X-ray laser light with a wavelength of 1.2 Angstroms. This light was created using SACLA, a cutting-edge X-ray Free Electron Laser (XFEL) facility unveiled by RIKEN in February 2011 in Harima, Japan. SACLA (SPring-8 Angstrom Compact free electron LAser) opens a window into the structure of atoms and molecules at a level of detail never seen before.

The use of ultra high-intensity X-ray free electron laser light to explore the miniature structure of matter, until recently inconceivable, is today transforming how we visualize the atomic world. By providing much shorter wavelengths and higher intensities than other lasers, XFEL enables researchers to directly observe and manipulate objects on an unrivalled scale, opening new research opportunities in fields ranging from medicine and drug discovery to nanotechnology.

One of only two facilities in the world to offer this novel light source, SACLA has the capacity to deliver radiation one billion times brighter and with pulses one thousand times shorter than other existing X-ray sources. In late March, the facility marked its first milestone with beam acceleration to 8GeV and spontaneous X-rays of 0.8 Angstroms.

Only three months later, SACLA has marked a second milestone. On June 7, SACLA successfully increased the density of the electron beam by several hundred times and guided it with a precision of several micrometers to produce a bright X-ray laser with a wavelength of only 1.2 Angstroms (a photo energy of 10 keV). This matches the record of 1.2 Angstroms set at the only other operational XFEL facility in the world, the Linac Coherent Light Source (LCLS) in the United States.

With experiments soon to commence and user operations at the facility to begin by the end of fiscal 2011, this new record offers a taste of things to come with SACLA's powerful beam, the world's most advanced X-ray free electron laser.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by RIKEN.

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

First telecommunications wavelength quantum dot laser grown on a silicon substrate

ScienceDaily (June 14, 2011) — A new generation of high-speed, silicon-based information technology has been brought a step closer by researchers in the Department of Electronic and Electrical Engineering at UCL and the London Centre for Nanotechnology. The team's research, published in the journal Nature Photonics, provides the first demonstration of an electrically driven, quantum dot laser grown directly on a silicon substrate (Si) with a wavelength (1300-nm) suitable for use in telecommunications.

Silicon is the most widely used material for the fabrication of active devices in electronics. However, the nature of its atomic structure makes it extremely hard to realise an efficient light source in this material.

As the speed and complexity of silicon electronics increases, it is becoming harder to interconnect large information processing systems using conventional copper electrical interconnects. For this reason the field of silicon photonics (the development of optical interconnects for use with silicon electronics) is becoming increasingly important.

The ideal light source for silicon photonics would be a semiconductor laser, for high efficiency, direct interfacing with silicon drive electronics and high-speed data modulation capability. To date, the most promising approach to a light source for silicon photonics has been the use of wafer bonding to join compound semiconductor laser materials from which lasers can be made to a silicon substrate.

Direct growth of compound semiconductor laser material on silicon would be an attractive route to full integration for silicon photonics. However, the large differences in crystal lattice constant between silicon and compound semiconductors cause dislocations in the crystal structure that result in low efficiency and short operating lifetime for semiconductor lasers.

The UCL group has overcome these difficulties by developing special layers which prevent these dislocations from reaching the laser layer together with a quantum dot laser gain layer. This has enabled them to demonstrate an electrically pumped 1,300 nm wavelength laser by direct epitaxial growth on silicon. In a recent paper in Optics Express (Vol. 19 Issue 12, pp.11381-11386 (2011)) they report an optical output power of over 15 mW per facet at room temperature.

In related work the group, working with device fabrication colleagues at the EPSRC National Centre for III-V Technologies, have demonstrated the first quantum dot laser on a germanium (Ge) substrate by direct epitaxial growth. The laser, reported in Nature Photonics , (DOI: 10.1038/NPHOTON.2011.120, 12 June 2009) is capable of continuous operation at temperatures up to 70 deg. C and has a continuous output power of over 25 mW per facet.

Leader of the epitaxy research that enabled the creation of these lasers and Royal Society University Research Fellow in the UCL Department of Electronic and Electrical Engineering, Dr Huiyun Liu, said: "The use of the quantum dot gain layer offers improved tolerance to residual dislocations relative to conventional quantum well structures. Our work on germanium should also permit practical lasers to be created on the Si/Ge substrates that are an important part of the roadmap for future silicon technology."

Head of the Photonics Group in the UCL Department of Electronic and Electrical Engineering, Principal Investigator in the London Centre for Nanotechnology and Director of the EPSRC Centre for Doctoral Training in Photonic Systems Development, Professor Alwyn Seeds, said: "The techniques that we have developed permit us to realise the Holy Grail of silicon photonics -- an efficient, electrically pumped, semiconductor laser integrated on a silicon substrate. Our future work will be aimed at combining these lasers with waveguides and drive electronics leading to a comprehensive technology for the integration of photonics with silicon electronics."

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University College London - UCL.

Journal References:

Huiyun Liu, Ting Wang, Qi Jiang, Richard Hogg, Frank Tutu, Francesca Pozzi, Alwyn Seeds. Long-wavelength InAs/GaAs quantum-dot laser diode monolithically grown on Ge substrate. Nature Photonics, 2011; DOI: 10.1038/nphoton.2011.120Ting Wang, Huiyun Liu, Andrew Lee, Francesca Pozzi, Alwyn Seeds. 13-µm InAs/GaAs quantum-dot lasers monolithically grown on Si substrates. Optics Express, 2011; 19 (12): 11381 DOI: 10.1364/OE.19.011381Huiyun Liu, Ting Wang, Qi Jiang, Richard Hogg, Frank Tutu, Francesca Pozzi, Alwyn Seeds. Long-wavelength InAs/GaAs quantum-dot laser diode monolithically grown on Ge substrate. Nature Photonics, 2011; DOI: 10.1038/nphoton.2011.120

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