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Li H.,Stanford PULSE Institute | Li H.,Stanford University | Li H.,SLAC | Chen L.-J.,Idesta Quantum Electronics | And 13 more authors.
Optics Letters | Year: 2014

Using balanced detection in both the radio frequency (RF) and the optical domain, we remotely synchronize the repetition rate of a Ti:sapphire oscillator to an Er-doped fiber oscillator through a 360mlength-stabilized dispersion compensated fiber link. The drift between these two optical oscillators is 3.3 fs root mean square (rms) over 24 hours. The 68 MHz Er-doped fiber oscillator is locked to a 476 MHz local RF reference clock, and serves as a master clock to distribute 10 fs-level timing signals through stabilized fiber links. This steady remote two-color optical-to-optical synchronization is an important step toward an integrated femtosecond fiber timing distribution system for freeelectron lasers (FELs); it does not require x-ray pulses, and it makes sub-10-fs optical/x-ray pump-probe experiments feasible. © 2014 Optical Society of America. Source


News Article
Site: http://phys.org/physics-news/

Hasan DeMirci, a SLAC scientist with the Stanford PULSE Institute who teamed up with graduate student Raymond Sierra on the new system, has been using the Linac Coherent Light Source (LCLS) X-ray laser – a DOE Office of Science User Facility – to zero in on the details of ribosomes at work. In addition to their universal role in deciphering the genetic code to build proteins, ribosomes are also important targets for antibiotic treatments. It is difficult to form ribosomes into crystals so they can be studied with X-rays because they are very fragile. The new system sprang from a desire to better preserve the ribosome crystals. The research team did this by keeping the tiny crystals in the same solution they were grown in at temperatures approaching those in their natural environment, and by finding a more gentle way to deliver or "inject" them into a vacuum chamber, where they are struck by LCLS X-ray pulses. The new system, dubbed coMESH, uses low-cost, off-the-shelf components to shape and protect a stream of crystallized proteins with a surrounding stream of electrically charged fluid. It was successfully tested in a 2014 experiment and featured in the Nov. 30 online edition of Nature Methods. "Our strategy was to come up with an injector that can handle anything, not just ribosomes," DeMirci said. "We are addressing a definite need in the scientific community for a more universal way to deliver samples to LCLS." In addition to demonstrating that the new system worked, the experiments also gave the scientists a more detailed, 3-D look at how one component of the ribosome binds to an antibiotic called paromomycin that is used to treat parasitic infections. "Now we have a more realistic picture of how this antibiotic interacts with ribosomes at temperatures close to those in their natural environment," DeMirci said. The new system consists of a thin tube, about one-tenth of a millimeter in diameter, inside a slightly larger tube; the sizes can vary based on the dimensions of the crystal samples. A charging electrode applies low electrical current to the fluid in the larger tube, which focuses the flow to a thin filament. Both tubes end at the same point and the electrical current in the outer fluid greatly narrows both streams of fluid as they emerge from the tubes. The system is also designed to waste fewer crystals in experiments than some other sample delivery methods. The thickness and flow rate of the inner stream can be fine-tuned by changing the applied voltage and the width of the tubing to maximize the rate at which X-ray pulses strike the crystals flowing into their path. DeMirci and Sierra said that based on the 3-D atomic-scale details they were able to see in the ribosome-drug complex and in samples of a photosynthetic protein complex known as photosystem-II, it doesn't appear the voltage damaged the protein structures. "It's like birds sitting on an electrical wire," DeMirci said. DeMirci and Sierra said they expect the coMESH system will find wider use by other scientists conducting experiments at LCLS. "We want this to be 'plug-and-play,'" Sierra said, "so all they have to think about during their experiment is collecting data and not troubleshooting sample delivery." Explore further: New tool puts LCLS X-ray crystallography on a diet More information: Raymond G Sierra et al. Concentric-flow electrokinetic injector enables serial crystallography of ribosome and photosystem II, Nature Methods (2015). DOI: 10.1038/nmeth.3667


News Article
Site: http://www.rdmag.com/rss-feeds/all/rss.xml/all

Researchers at the Department of Energy's SLAC National Accelerator Laboratory have found a simple new way to study very delicate biological samples – like proteins at work in photosynthesis and components of protein-making machines called ribosomes – at the atomic scale using SLAC's X-ray laser. Hasan DeMirci, a SLAC scientist with the Stanford PULSE Institute who teamed up with graduate student Raymond Sierra on the new system, has been using the Linac Coherent Light Source (LCLS) X-ray laser – a DOE Office of Science User Facility – to zero in on the details of ribosomes at work. In addition to their universal role in deciphering the genetic code to build proteins, ribosomes are also important targets for antibiotic treatments. It is difficult to form ribosomes into crystals so they can be studied with X-rays because they are very fragile. The new system sprang from a desire to better preserve the ribosome crystals. The research team did this by keeping the tiny crystals in the same solution they were grown in at temperatures approaching those in their natural environment, and by finding a more gentle way to deliver or "inject" them into a vacuum chamber, where they are struck by LCLS X-ray pulses. The new system, dubbed coMESH, uses low-cost, off-the-shelf components to shape and protect a stream of crystallized proteins with a surrounding stream of electrically charged fluid. It was successfully tested in a 2014 experiment and featured in the Nov. 30 online edition of Nature Methods. "Our strategy was to come up with an injector that can handle anything, not just ribosomes," DeMirci said. "We are addressing a definite need in the scientific community for a more universal way to deliver samples to LCLS." In addition to demonstrating that the new system worked, the experiments also gave the scientists a more detailed, 3-D look at how one component of the ribosome binds to an antibiotic called paromomycin that is used to treat parasitic infections. "Now we have a more realistic picture of how this antibiotic interacts with ribosomes at temperatures close to those in their natural environment," DeMirci said. The new system consists of a thin tube, about one-tenth of a millimeter in diameter, inside a slightly larger tube; the sizes can vary based on the dimensions of the crystal samples. A charging electrode applies low electrical current to the fluid in the larger tube, which focuses the flow to a thin filament. Both tubes end at the same point and the electrical current in the outer fluid greatly narrows both streams of fluid as they emerge from the tubes. The system is also designed to waste fewer crystals in experiments than some other sample delivery methods. The thickness and flow rate of the inner stream can be fine-tuned by changing the applied voltage and the width of the tubing to maximize the rate at which X-ray pulses strike the crystals flowing into their path. DeMirci and Sierra said that based on the 3-D atomic-scale details they were able to see in the ribosome-drug complex and in samples of a photosynthetic protein complex known as photosystem-II, it doesn't appear the voltage damaged the protein structures. "It's like birds sitting on an electrical wire," DeMirci said. DeMirci and Sierra said they expect the coMESH system will find wider use by other scientists conducting experiments at LCLS. "We want this to be 'plug-and-play,'" Sierra said, "so all they have to think about during their experiment is collecting data and not troubleshooting sample delivery."


In one experiment, a team led by Lindenberg showed atoms shifting in trillionths of a second to produce a wrinkle in a 3-atom-thick sample of a material that might someday be used in flexible electronics. Another study observed semiconductor crystals—called "quantum dots" because they defy classical physics at the nanoscale—expand and shrink in response to ultrafast pulses of laser light. Revealing such intriguing properties at the nanoscale gives clues about the fundamental nature of materials and how they perform in applications we rely on for energy or information. "Even though some of these materials are completely embedded in everyday technologies, not a lot is understood about how they work," says Lindenberg, who is an associate professor of materials science and engineering and of photon science. He is also a principal investigator for two SLAC/Stanford joint institutes—Stanford Institute for Materials and Energy Sciences and Stanford PULSE Institute. "Part of the reason some phenomena are not well understood is because they happen so fast – in billionths, trillionths or even quadrillionths of a second. For the first time, we have tools that allow us to see these things," he says. Working at the intersection of materials science and engineering, Lindenberg and his team have a particular focus on finding promising materials for next-generation electronics, light-based data storage technologies and energy applications. "There are a broad range of new properties that emerge at the nanoscale," Lindenberg says. "The tiniest samples, with just tens or hundreds of atoms, can have nearly flawless structures that make them ideal test tubes for very fundamental questions about what happens when a material transforms." The team uses different types of laser light at SLAC and Stanford labs to learn how simple tweaks in the size, shape and design of materials can change their basic properties in unexpected ways, which could lead to new applications. Taking advantage of the powerful X-rays at SLAC facilities, including the Linac Coherent Light Source and the Stanford Synchrotron Radiation Lightsource, they explore ultrafast changes in nanoscale samples. "We are trying to understand how electrons or atoms move in materials, which in turn determines, for example, the efficiency of solar cells and other energy-related materials, and how materials switch between different forms," he says. "Ultrafast techniques allow you to see these kinds of things in a completely new way." Explore further: Scientists use LCLS to see photovoltaic process in action


Allaria E.,Elettra - Sincrotrone Trieste | Diviacco B.,Elettra - Sincrotrone Trieste | Callegari C.,Elettra - Sincrotrone Trieste | Finetti P.,Elettra - Sincrotrone Trieste | And 57 more authors.
Physical Review X | Year: 2014

The two single-pass, externally seeded free-electron lasers (FELs) of the FERMI user facility are designed around Apple-II-type undulators that can operate at arbitrary polarization in the vacuum ultraviolet-to-soft x-ray spectral range. Furthermore, within each FEL tuning range, any output wavelength and polarization can be set in less than a minute of routine operations. We report the first demonstration of the full output polarization capabilities of FERMI FEL-1 in a campaign of experiments where the wavelength and nominal polarization are set to a series of representative values, and the polarization of the emitted intense pulses is thoroughly characterized by three independent instruments and methods, expressly developed for the task. The measured radiation polarization is consistently > 90% and is not significantly spoiled by the transport optics; differing, relative transport losses for horizontal and vertical polarization become more prominent at longer wavelengths and lead to a non-negligible ellipticity for an originally circularly polarized state. The results from the different polarimeter setups validate each other, allow a cross-calibration of the instruments, and constitute a benchmark for user experiments. Source

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