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Showing posts with label Linac Coherent Light Source. Show all posts
Showing posts with label Linac Coherent Light Source. Show all posts
A series of movies shows how increasing flows of gas that shape a stream of liquid affects the formation of liquid sheets and their soap-bubble-like sheen. Credit: SLAC National Accelerator Laboratory
Water is an essential ingredient for life as we know it, making up more than half of the adult human body and up to 90 percent of some other living things. But scientists trying to examine tiny biological samples with certain wavelengths of light haven't been able to observe them in their natural, watery environments because the water absorbs too much of the light. Now there's a way around that problem: A team led by scientists at the Department of Energy's SLAC National Accelerator Laboratory turned tiny liquid jets that carry samples into the path of an X-ray beam into thin, free-flowing sheets, 100 times thinner than any produced before. They're so thin that X-rays pass through them unhindered, so images of the samples they carry come out clear.
The new method opens new windows on critical processes in chemistry, physics and biology, including the nature of water itself, the researchers said in an April 10 report in Nature Communications.
The method was developed at SLAC's X-ray free-electron laser, the Linac Coherent Light Source (LCLS), but they said it can also work in experiments with synchrotron light sources, tabletop lasers and electron beams.
"This opens up possibilities in a lot of fields," said SLAC staff scientist Jake Koralek, who led the research with Daniel DePonte, leader of the LCLS Sample Environment Department.
"Until now, we haven't been able to examine samples suspended in water with two types of light – infrared and 'soft', lower-energy X-rays – that are important for making images and using spectroscopy to study basic processes in physics, chemistry and biology, including the physics of water," Koralek said.
"The new nozzle we developed, which can create flowing sheets of liquid just 100 water molecules thick that persist for days in a vacuum, solves that problem. The sheets can even be used to image samples with electron beams that resolve even smaller details."
Shaping Liquid with Gas
The nozzle is a tiny glass chip with three microscopic channels. A stream of liquid flows through the middle channel, shaped by flows of gas coming in from the channels on either side. This particular nozzle was made with photolithography, a technique used
These images show the formation of tiny sheets of liquid shaped by jets of gas from a nozzle developed at SLAC. Top: As the gas flow increases, the liquid sheets become bigger. Bottom: The nozzle produces a series of liquid sheets; the one closest to the nozzle is the widest and thinnest. Each sheet is perpendicular to the previous one, so we are seeing the second and fourth sheets from the side. Credit: SLAC National Accelerator Laboratory
As the scientists turn up the speed of the gas flow, the liquid stream spreads into a series of sheets whose width and thickness can be precisely controlled. The sheet closest to the nozzle is the widest and thinnest; the farther they get from the nozzle, the narrower and thicker the sheets become until they finally merge into a cylindrical stream. The sheets shimmer like soap bubbles in a variety of colors, the result of light reflecting off both the front and back surfaces of the sheet. And just as the contour lines on a topographic map mark differences in elevation, the hue and spacing of a sheet's ever-changing bands of color indicate how thick it is and how much the thickness changes from one point to another.
"It's a very flexible and reliable design for creating both ultrathin and slightly thicker liquid sheets, which can be desirable for some applications" said Linda Young, a distinguished fellow at DOE's Argonne National Laboratory and professor at the University of Chicago who was not involved in the study.
She said she will be using the nozzle to make slightly thicker sheets of water for an LCLS study of how water molecules behave after one of their electrons has been ripped away. These ionized water molecules persist for only a few hundred femtoseconds, or millions of a billionth of a second, and "the X-rays provide a completely new and clean wayto monitor their electronic response in their natural environment, so that's why we're excited about it," Young said.
A new way to study extreme forms of water
The liquid sheets have already been used in experiments that explore the properties of water in extreme environments like those on giant planets, said co-author Siegfried Glenzer, a SLAC professor and head of the lab's High Energy Density Science Division.
Those experiments were performed with the FLASH free-electron laser at Germany's Deutsches Elektronen-Synchrotron (DESY). Researchers used X-ray pulses to heat the liquid sheets to thousands of degrees to simulate the extremely warm, dense form of water present in giant planets like Jupiter. Then they measured the reflectivity and conductivity of the super-hot water with optical laser pulses in the instant before the water vaporized. These measurements could only be made on a flat sheet of water.
"There are many mysteries in those big planets and they're important for understanding the evolution of our planetary system as well as others," Glenzer said. "This is a beautiful tool for studying water itself, and in the future we will also study other materials that we can mix into it."
The team measured the thickness of the sheets with a beam of infrared light at the Advanced Light Source at the DOE's Lawrence Berkeley National Laboratory, and also demonstrated that the sheets could be used for infrared spectroscopy, where light absorbed by a material reveals its chemical makeup.
Certain chemical reactions occur at a higher rate when the reactants are stuck to a two-dimensional surface. But sometimes the desired reaction competes with other processes. To control the surface chemistry, Jerry LaRue, from the SLAC National Accelerator Laboratory in California, and his colleagues demonstrate a new technique in which pulses of light in the terahertz frequency range selectively drive an oxidation reaction on a metal surface. The pulses effectively gives a kick to adsorbed oxygen atoms, so that they move along the surface and interact with other molecules more often.
The surface reaction studied by LaRue et al. is the conversion of carbon monoxide (CO) and oxygen into carbon dioxide (CO2). This oxidation process is commonly performed in a car’s catalytic converter, where metals serve as the surface catalyst. The researchers looked specifically at ruthenium—a relatively inexpensive catalyst material but one in which CO oxidation must compete with CO desorbing from the surface.
Previous work showed that optical pulses could increase CO oxidation on ruthenium, but the pulses also heat the surface, causing increased desorption. In their experiments, LaRue and his colleagues utilized terahertz pulses produced at SLAC’s Linac Coherent Light Source. The team showed that the electric field from the pulses causes electrons to oscillate near the surface, and this electron motion weakens the bonds that hold oxygen atoms to the metal. The partly released oxygen atoms have extra energy for moving along the surface and colliding with COmolecules forming CO2. The terahertz pulses do not increase the surface temperature, so the CO desorption rate remains unchanged. The researchers found that terahertz stimulation led to as much as a third of adsorbed COconverting to CO2.
Principle of the experiment. The motion of the magnetic moments in TbMnO3 (shown as arrows on the right hand side) is excited by a terahertz pulse (red beam) and probed by a pulse from the x-ray laser LCLS (blue beam). Credit: Teresa Kubacka
Data on a hard drive is stored by flipping small magnetic domains. Researchers from the Paul Scherrer Institute PSI and ETH Zurich have now changed the magnetic arrangement in a material much faster than is possible with today's hard drives. The researchers used a new technique where an electric field triggers these changes, in contrast to the magnetic fields commonly used in consumer devices. This method uses a new kind of material where the magnetic and electric properties are coupled. Applied in future devices, this kind of strong interaction between magnetic and electric properties can have numerous advantages. For instance, an electrical fieldcan be generated more easily in a device than a magnetic one. In the experiment, the changes in magnetic arrangement took place within a picosecond (a trillionth of a second) and could be observed with x-ray flashes at the Americanx-ray laserLCLS. The flashes are so short that you can virtually see how the magnetisation changes from one image to the next - similar to how we are able to capture the movement of an athlete with a normal camera in a series of images with a short exposure time. In future, such experiments should also be possible at PSI's new research facility, the x-ray laser SwissFEL.
The results will be published in the journal Science. They appear online in advance of print in Science Express on 6 March.
One common method of data storage uses materials in which different magnetic domains can be oriented in different directions. In other words, the tiny elementary magnets inside the material are aligned along two possible directions, which enables one bit to be saved in the material. A bit is the smallest unit of information, for which there are two possibilities, often referred to as 0 and 1. In the storage device, these correspond to the two different magnetic directions. In a real hard drive, which must store a large amount of information, there are many small areas that correspond to single bits. To change the information on the hard drive, the direction of the magnetism in one domain must be flipped. In modern consumer devices this is achieved using a small magnetic field.
An electric field can be generated in a small space more easily than a magnetic field, which means that, in principle, smaller storage devices can be constructed if magnetism is switched by electric fields. A strong connection between magnetic and electric properties is exhibited by so-called multiferroic materials, which have been one of the hottest topics in materials research for a number of years. Researchers from the Paul Scherrer Institute PSI and ETH Zurich have now studied the material TbMnO3 and demonstrated that its magnetic arrangement can be changed by an electric field in a matter of picoseconds (10-12 s = one trillionth of a second), which is considerably shorter than the time it takes for today's hard drives to be switched. "This shows that multiferroic materials can be switched quickly enough electrically for them to be used in magnetic storage devices," explains Urs Staub, a research group leader at PSI and one of the research project supervisors. "Electric switching could have numerous advantages. In order to generate a magnetic field, you need a coil through which a current flows. An electric field can be generated without current.
"The material we studied can't be used in technical devices - you need very low temperatures and strong electrical fields to observe the relevant phenomena. However, the basic result probably also applies for materials that are more suitable for applications and will presumably consist of a combination of thin layers of different materials."
Exposure time: 0.000 000 000 000 1 seconds
The arrangement of magnetic moments in TbMnO3.Neighbouring moments are tilted in respect to each other. There are two possible directions in which the moments can turn that might correspond to the two values of a bit in future storage …more
The experiment is based on the interaction between pulsed light produced by two lasers - terahertz light generated by a laser which can easily fit into a lab, and the radiation from the x-ray laser Linac Coherent Light Source (LCLS), a large-scale research facility located at SLAC National Accelerator Laboratory in Menlo Park, California, that is roughly three kilometres in length. In the experiment, the material was illuminated with short flashes of terahertz-frequency light which were only a few picoseconds long. Light consists of an electric and a magnetic field, which periodically become stronger and weaker. The terahertz flashes were so short that the electric fields in them were only able to perform a few oscillations. With experiments at the LCLS, the researchers were able to demonstrate that the magnetic arrangement was distorted by the flash of light and - with a slight delay - this distortion followed the oscillation of the electrical field within the flash. The magnetic component of the light was too weak to influence the magnetic structure. The x-ray laser generates very short (100 femtoseconds = 0.000 000 000 000 1 seconds) and intense flashes of x-ray light which are so much shorter than the terahertz flash. This allows the x-rays to measure the magnetic distortion along the different stages of its motion, similar to how a camera with a fast shutter speed captures still images of rapid motions. Today, the LCLS is one of two facilities where such experiments are possible. In the future, they will also be possible at the x-ray laser SwissFEL, which is currently under construction at the Paul Scherrer Institute. "An experiment like this can only be conducted at an x-ray laser because only the pulses from the x-ray laser show the magnetic order and are short enough for you to follow the chronological sequences," explains Staub.
Tilted elementary magnets
Magnetic materials which can be used to store data can have different magnetic arrangements. In today's hard drives, the magnetic areas are arranged ferromagnetically, which means that the elementary magnets or, to use the technical term, magnetic moments are all pointing in same direction within the area encoding one bit. In the material studied in the experiment, the moments are arranged in rows but in such a way that two neighbouring moments are slightly rotated with respect to each other as opposed to being parallel. If you move from one moment to the next, the direction of the moments keeps turning and overall the sequence of magnetic moments forms a cycloid. Generally speaking, there are two directions in which the moments can turn, clockwise and anticlockwise - and these could correspond to the two values of a bit. To change between "0" and "1", the magnetic moments would have to change the turning direction within the sequence, which is equivalent to rotating the entire sequence of magnetic moments by 180 degrees.
Positive and negative - offset from each other
The multiferroic material also has another property: electric polarisation, which means that the positive and negative charges are shifted slightly against each other. The interior of the material is constructed from atoms that have fixed positions in a three-dimensional structure. As there are just as many negative charges (electrons) as positive ones (atomic nuclei) in the atoms, the entire material is electrically neutral. Some of the electrons, however, are not bound rigidly to the atomic nuclei. These electrons can be displaced with respect to the atomic nuclei, which means that one side of the material is positively charged, the other negatively. In other words, the material is electrically polarised. In everyday life, electrically polarised materials are primarily known thanks to the piezoelectric effect used to produce sparks in lighters or sound in loudspeakers, for instance.
Electrically and magnetically linked
The deflection of the magnetic moments (black line) follows the electric field of the terahertz pulse (red line) with a short delay. The blue dots show the results of the measurement. Credit: Kubacka et al., Science Express (2014) DOI: 10.1126/science.1242862
In TbMnO3, the electrical polarisation is linked to the magnetic arrangement, which means that if the magnetic moments turn in one direction, this always corresponds to an alignment of the electric polarisation; if you reverse the polarisation, the rotational direction of the magnetic moments also turns around. The researchers studied this coupling in their experiment. Using the alternating electric field of the terahertz pulse, they influenced the electric polarisation and observed the extent to which the magnetic arrangement followed the alternating field. Although the electric field was too weak to actually turn the sequence of magnetic moments by 180 degrees, the scientists were able to observe that it was turned by around four degrees in time with the electrical field. "This procedure is also important for possible applications," explains Teresa Kubacka, a doctoral student in the Ultrafast Dynamics Group at ETH Zurich and first author of the paper. "The terahertz pulse is designed in such a way that it influences the magnetic arrangement only in this particular way. If the magnetic arrangement in a device could be changed so specifically, much less energy would be wasted and the material would not heat up as much."
Precision measuring
It is the first time that it was possible to measure such a rapid change in a multiferroic material so precisely. The angle by which the magnetic moments were turned was determined using the short flashes from the LCLS x-ray laser in a scattering experiment. It involved sending the x-ray beam through the sample studied and observing the directions in which the x-ray light was deflected by the sample. In the case of this material, there are directions in which the light is deflected by the atomic structure and others where the deflection is caused by the magnetic moments. If the magnetic arrangement is changed, the intensity of the deflected x-ray light changes. In the experiment, the researchers measured the intensity of the deflected x-ray beam at different times for a selected direction. Then they calculated how the magnetic moments react to the electric field within the terahertz flash.
Experimental challenges
"One of the challenges of the experiment was to create the terahertz flashes with the correct frequency and guarantee that enough of their intensity reaches the sample. Such pulses were not created directly by a laser, but rather with the aid of special organic crystals hit by laser pulses with another frequency. At ETH Zurich, we are also working on facilities that generate terahertz pulses and working together with the specialists from PSI and LCLS we were able to adapt the lasers available at the LCLS to our experiment's needs," says Kubacka.
Joe Robinson, a staff scientist, at left, works with Mike Minitti, group leader for LCLS-related lasers, on a laser system to be used in an LCLS experiment. Credit: Matt Beardsley by Glenn Roberts Jr.
http://phys.org/news/2013-02-array-lasers-slac.html#jCp In less than a decade, SLAC has built up an impressive array of dozens of laser systems – and a team of laser scientists and engineers – with capabilities that make it one of the most cutting-edge national laboratories under the U.S. Department of Energy. Lighting the way SLAC's newfound laser focus took shape with the 2005 hire of Bill White, a laser expert who had worked at Lawrence Livermore National Laboratory and in private enterprise. White was hired to help the lab prepare for the 2009 launch of the Linac Coherent Light Source, a unique X-ray laser with ultrabright, ultrashort pulses that requires more conventional lasers for most experiments. The lab's inventory of 135 high-power optical lasers includes 40 lasers that can be used in LCLS experiments. Another 18 lasers are installed at the LCLS injector, where they produce the beam of electrons that is converted into X-ray pulses. There are 25 laser facilities at SLAC, and their laser systems serve in a variety of roles in experiments: aligning molecules in the same direction and orientation, shocking and compressing matter, switching magnetic states and exciting chemical reactions, as examples. The lasers often incorporate off-the-shelf commercial components, though SLAC's specialization in studying ultrafast processes, which can be measured in trillionths to quadrillionths of a second, requires customization, White said. SLAC's laser systems, at their core, represent "controlled energy that can interact with matter in countless ways," said Alan Fry, deputy director of SLAC's Laser Science and Technology Division. "They allow us to stimulate very specific changes in materials and to probe and measure those changes with extreme precision." White grew SLAC's laser team from a staff of three into a division with 15 full-time staff, including laser scientists, laser engineers and engineering physicists; as well as several full-time students and post-doctoral researchers. The student researchers benefit from in-house laser expertise, Fry said. The bulk of the growth was in the past three years, since LCLS began operating, and the laser team will grow more with the LCLS-II project, which will multiply SLAC's X-ray laser experiments. Growing role, recognition for laser group While the laser division supports all of the LCLS-related lasers, its role in designing, installing, tuning, operating, maintaining and repairing lasers extends across the lab and Stanford, and even to other research facilities. From the start, the laser group has had a mission to "support laser science anywhere that needed it" at SLAC, White said. The lab's laser specialists have collaborated in laser research and development work at Lawrence Berkeley and Argonne national labs, among others.
Credit: Laser components description courtesy of Mike Woods/SLAC. Laser diagram courtesy of Lakkasuo/Wikimedia Commons Conventional optical lasers require three components: 1) a "pump source," such as a flashlamp or other laser that provides an energy source; 2) a "lasing medium," such as a specialized crystal that amplifies light; and 3) an "optical resonator," which is a cavity with two end mirrors, one an end mirror that is highly reflective and the other an output mirror that partially transmits light, allowing light to circulate within the resonator. In July 2012, a U.S. Department of Energy review committee commended SLAC's laser program for its scientific depth, technical and engineering quality, safety controls and user support, and stated that these achievements are "even more impressive in light of the fact that this is a relatively young program that has been initiated from scratch in a laboratory without a history or tradition of laser research." Laser division managers are now working to extend SLAC's unique laser expertise and make its laser systems available to an even broader community of researchers. SLAC's most energetic laser system is a two-beam long-pulse laser installed last year at LCLS to create superhot condensed matter. And this year the laser crew will help build the lab's highest-power laser – with a peak power of 10 trillion watts – to test next-generation accelerator technologies. Lasers on demand Mike Minitti, group leader for LCLS-related lasers, said scientists who use the LCLS "take a strong interest" in the lab's laser systems, which are integral to about 70 percent of all LCLS experiments. Users communicate regularly with laser staff about their needs for upcoming experiments, and in some cases undergo the extensive training required to operate lasers. And the laser staff pride themselves on serving the science needs of LCLS users. "I have yet to see an experiment be denied because we can't deliver a laser parameter," Minitti said. Most lasers at LCLS are used in "pump-probe" experiments, in which a laser beam induces a change in a sample that can be probed with another laser. Most critical to the function of LCLS' laser systems are timing and synchronization with the X-ray laser pulses, he said. "It's pretty awesome to see things work as well as they do," he said, including synchronizing lasers that are a mile and a half apart to fire within quadrillionths of a second of each other. "Some lasers need other lasers to run," Minitti added, like a Russian nesting doll, with one laser embedded in another and functioning as a single laser system.. Tuning and automation The type of laser light required for experiments at SLAC can cover the full spectrum, from visible light into infrared, ultraviolet and terahertz wavelengths. Philippe Hering, group leader for accelerator laser systems, said tuning a laser's wavelength is "kind of like a radio at home: you can change to different stations." Hering's team works with lasers that generate the electron beam used to produce the X-ray pulses. Staff at SLAC's Main Control Center can monitor and remotely control how those source lasers are functioning in real time, Hering said, and "They can change the laser spot size and pulse energy to optimize the electron beam produced," with built-in redundancies to minimize down time. "Lasers are now a core competency at LCLS, and are centrally important to many areas of the lab's mission, from accelerator science to X-ray science to materials science and chemistry," said Fry, "and we look forward to building on that expertise." Provided by SLAC National Accelerator Laboratory
