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Students Get a Taste of ALS User Experience Print

A group of seventh graders from Black Pine Circle (BPC) school in Berkeley recently had a rare opportunity to experience the ALS as “users” via a scientific research proposal project and field trip. The students were led by science and technology teacher Christine Mytko, who spent the past summer at the ALS through the Industry Initiatives for Science and Math Education (IISME) program. Mytko’s time at the ALS was focused on 3D imaging and printing techniques.

An integral part of the ISME program is educators taking their experiences back to the classroom through new curriculum development. As such, Mytko put together a program that would engage her students in collaborative proposal process similar to a typical ALS user proposal. Students worked in groups to craft proposals for scanning items of interest at the tomography beamline, a selection of which were chosen through a peer-review process and then scanned at Beamline 8.3.2. ALS beamline scientist Dula Parkinson worked with Mytko to develop the program and gave feedback on the kids’ proposal, which Mytko says was thrilling for her students.


The project culminated with a field trip to the ALS for all seventh graders, which included a visit to the ALS data visualization room, a diffraction demonstration, a beamline tour, and informative sessions about x-rays and tomography presented by ALS scientists. Students also got the chance to scan their winning proposals—which included the bone structure of a bird beak, a pop rock, duct tape, an eggshell, a butterfly wing, and agar—at Beamline 8.3.2 with Parkinson’s help. The data will go back to the classroom for the students to study and potentially use with their 3D printer.

“This is the first time we’ve done a trip like this at BPC, and actually in my whole teaching career,” says Mytko. “My experience here at the ALS has really transformed what I teach in 7th grade.”

See more photos from the students' trip to the ALS here.

Watch an ALS video about the project here.

Read teacher Christine Mytko's blog about her students' science and technology adventures.

 
Synchrotron Education Collaboration Print

synchrotron collaboration The Synchrotron Education Collaboration held its first meeting October 20-22 at Synchrotron Soleil, in St Aubain, France. The symposium, "Student Science at Synchrotrons: Educating the Next Generation of Scientists," was attended by scientists, educators, as well as representatives from eight synchrotrons. Participants listened to several presentations about current practices in engaging middle- and high-school students in science through hands-on activities including beamline experiments, visits to synchrotrons, and discussions with scientists. From the presentations, and input from other synchrotron facilities, a survey has been created to send to all light source facilities in order to assess the which best practices in education

This collaboration, funded by a grant from the France-Berkeley Fund, comprises representatives from the ALS, Soleil, and ESRF with the goal of developing an engaging and effective educational program for high-school students that will introduce them to the opportunities and challenges of scientific research with the intention of attracting and developing the next generation of young scientists. In particular,  there is a focus on strategies to engage students that are underrepresented in science by gender, race, and economic status.

Participants in this first symposium included representatives from light sources in France, Canada, Australia, Japan, the United States, and Italy; the next meeting will be the day preceding the AAAS in Chicago. Anyone interested in participating in the project should contact Elizabeth Moxon (ALS) or Claus Habfast (ESRF).

 
ALS 20th Anniversary Celebration Print

The 20th anniversary of the ALS was celebrated on Friday, October 4, with style, good humor, lots of stories, and a very large cake. More important, however, was the large number of current and former colleagues and users, who were delighted to have the opportunity to visit and catch up with former workmates. When not chatting with colleagues or listening to the high-shool chamber trio, attendees were entertained by a video montage, old photos featuring ALS staff and users through the years, and a four-paneled timeline.

Left: A memorable moment occurred when four Berkeley Lab directors (from leftDave Shirley, Charles Shank, Paul Alivisatos, and Andrew Sessler) joined ALS division director Roger Falcone (center) in cutting a ceremonial cake.

Here are some of the photos of the event; more will be posted on the ALS Facebook and Flickr pages.

 

 
RAPIDD Gives ALS Users a Faster Path to Beam Time Print

ALS users are invited to check out our web pages detailing our new RAPIDD proposal process. This combined process for Rapid Access Proposals, Industry, and Director's Discretion beam time accommodates users who require limited but rapid access to the ALS. Proposals may be submitted at any time.

RAPIDD complements the existing six-month General User Proposal process, which remains the access mechanism of choice for users who require significant beam time for an extended program of research, or for those wanting to perform complex experiments involving setup or reorganization of equipment at a beamline.

The ALS structural biology community has been using RAPIDD for a year, with 160 proposals receiving beam time in that period. As of July 2013, RAPIDD access was extended to beamlines 7.3.3 (SAXS/WAXS), 8.3.2 (microtomography) and 11.3.1 (small molecule crystallography) and to users from industrial groups.

Turnaround for rapid access requests, from proposal submission to beam time, is expected to be just a few weeks. Proposals are peer-reviewed by at least two reviewers. Proposals are added to a waiting list for the relevant beamline. Proposals are scheduled for beam time by beamline staff according to score and proposal submission date. Users should be prepared for beam time scheduling at short notice. Please note that allocation of beam time will depend on the number of proposals submitted, and so rapid access cannot be guaranteed. Currently, 5 to 10 percent of beam time is reserved for rapid access on relevant beamlines, and this will be monitored and adjusted to ensure a balance between the needs of users applying through RAPIDD and the six-month process.

A very limited amount of beam time is reserved on some beamlines to accommodate urgent requests, exciting new ideas, or special circumstances. This time is designated as "Director Discretionary time" and is allocated by the ALS Division Director for Science. Potential users who want to request Director’s Discretionary beam time are now expected to submit their request using RAPIDD, and advised to contact the appropriate beamline scientist or the ALS division deputy for science, Steve Kevan, directly. It is expected that the same user group will not submit repeated Director’s Discretionary proposals.

Development of RAPIDD is an ongoing process and ALS is actively seeking user feedback. The aim is to provide a flexible mechanism for users to formally request access to ALS, ensuring simple and urgent experiments are scheduled in a timely manner. This e-mail address is being protected from spambots. You need JavaScript enabled to view it

 
2013 ALS User Meeting Highlights Print

This year’s ALS User Meeting launched with a welcome from Users’ Executive Committee Chair Corie Ralston and LBNL Director Paul Alivisatos. ALS Director Roger Falcone followed with a “state of the ALS” presentation that began with a reminder of the ALS mission, which he noted remains true even in the midst of a government shutdown: “Supporting users in doing outstanding science in a safe environment.” Falcone gave the 414 meeting attendees an update on the ALS beamlines, which included good news about increased user numbers thanks to the new RAPIDD access system, enhanced robotics, and remote capabilities. Falcone reflected that ALS metrics continue to represent our highly productive users—the number of journal articles and papers per user that come from ALS research have continued to grow in the past year. Looking forward, Falcone touched on how a proposed ALS upgrade to a diffraction-limited light source would increase scientific capabilities.

With DOE travel cancelled due to shutdown, the meeting’s scheduled DOE update was filled with a presentation by the Lab’s own government relations representative, Don Medley, on how to talk about science with elected representatives. Medley spoke about framing discussions with politicians in terms of the “value of our country’s science ecosystem.”

The keynote speaker series began with the director of Argonne National Lab’s Joint Center for Energy Storage Research (JCESR) George Crabtree—via video conference—speaking about the challenges and opportunities in energy storage science. Crabtree encouraged his audience of scientists to look beyond lithium ion batteries to the next generation of battery capabilities and presented numerous ways that synchrotron science can move that process forward. Next up was UC Berkeley’s Michael Eisen, who gave an engaging presentation on the transformation of scientific research communication. Eisen, a biologist and an associate professor of genetics, genomics, and development, is also the founder of the Public Library of Science (PLOS), which is a nonprofit publisher that seeks to make research publication more open and immediately available. Jim Krupnick, recently retired Berkleley Lab COO, then took the stage to reflect on the early days of the ALS and its construction history, especially appropriate in this 20th anniversary year. Krupnick regaled the audience with entertaining vignettes and rarely seen historical photos. UC Berkeley’s Jamie Cate gave the final keynote, which was focused on high-resolution structures of the ribosome, many of which were determined at the ALS.

ALS staff updates included User Services group lead Sue Bailey, who introduced the new ALS user portal and RAPIDD access system. Christoph Steier, deputy group leader of the ALS Accelerator Physics Group, gave an ALS accelerator update. Recent upgrades have improved brightness at the ALS by a factor of three, while storage ring RF upgrades and low-conductivity water upgrades have also been implemented this year. Looking to the future, Steier spoke about the dramatic improvements in brightness and coherence that would be possible with a diffraction-limited upgrade. The proposed ALS upgrade, termed ALS-II, would follow the trend of international user facility activity toward brighter storage rings. Steve Kevan, deputy division director for science at the ALS, went on to elaborate on how the ALS-II would benefit user science in general and various beamlines in particular.

Next up was the ever-popular student poster competition, followed by a reception that gave the 23 students a chance to field questions about their work and 34 exhibitors an opportunity to introduce their wares to users. First prize went to Royce Lam of UC Berkeley’s Saykally Group, for his research using x-ray absorption spectroscopy to probe ions in solution.

Tuesday morning featured this year’s David Shirley Award winner, North Carolina University’s Harold Ade, speaking about his achievements in polymer science. This year’s student poster award winner also had a chance to present and field questions about his research. The morning progressed with science highlight presentations by ALS users working in a variety of research areas.

Tuesday’s awards dinner was a celebratory gathering of ALS users recognizing exceptional synchrotron science. The Klaus Halbach Award for Innovative Instrumentation went to Chris Jozwiak of the Lab’s Materials Science Division and the Tim Renner User Services Award for Outstanding Support to the ALS User Community went to John Pepper of the ALS Mechanical Technology Division. Descriptions of the awards and more photos of the recipients will be posted soon.

 
Summer at the ALS = Opportunities for Teachers and Students Print

The ALS plays host to many teachers and students each summer, providing invaluable internship and research opportunities. Here’s a sampling of this summer’s visitors.

mytkoChristine Mytko (right), a middle school science and technology teacher at Black Pine Circle School in Berkeley, has been researching 3D imaging and printing techniques at Beamline 8.3.2 this summer through the Industry Initiatives for Science and Math Education (IISME) program. The program matches educators with scientific institutions to create research opportunities that benefit the teacher as an individual and students via new curriculum development. Mytko has been exploring new ways for her students to replicate the 3D printing process she’s been working with at the ALS, likely using an Xbox Kinect as a 3D scanner (instead of a synchrotron) to capture a series of 2D images that they can later reconstruct and print on their classroom 3D printer.  “My experience at the tomography beamline has also given me some great perspective on scale, which is something my students and I talk about a lot in science class,” says Mytko.  Mytko is looking forward to put size and scale into a practical context this fall, when her students will be writing proposals for the opportunity to scan their own samples during a scheduled visit to the ALS.

 

knightTom Knight (left), a chemistry and biology teacher at Vallejo High School, is also working at the ALS this summer through the IISME program.Knight has been involved with the ALS since 1998, when he came to the ALS to do summer research with Mike Martin at the infrared beamlines. In 2009 he helped build the high-resolution spectrometer at Beamline 5.4. This summer he’ll get his first chance to do some experiments with the spectrometer, olfactometry measurements of gas samples from wine bottles. Wine manufacturers already use infrared for quality control, measuring the actual wine, but Knight is interested in investigating whether anything can be learned from the gas. Knight has run the ALS high school internship program for the past three year and has also helped run teacher internship programs. “My experiences at the ALS has made a huge difference in how I teach science because I’ve had a chance to be immersed in a network of people who are actually doing science,” says Knight. “Most teachers don’t have that experience.”

 

potasapnOlivier Portaspana (left) is one of three French students interning at the ALS this summer from Ensicaen in Caen, a school that has a long history of sending interns to the Berkeley Lab and the ALS. Portaspana is currently enrolled in the first year of a master’s program in engineering, focusing on advanced instrumentation. He’s been working on visual tomography at Beamline 5.4, reconstructing 3D pictures of samples and looking at various techniques for improving accuracy.

 

zhangUC Berkeley undergraduate bioengineering student Jason Zhang (right) is spending the summer interning at the ALS through the Cal Energy Corps, an undergraduate internshipprogram that focuses on sustainable energy research and projects around the world. Zhang has been working at Beamline 8.3.2 on a project to improve methods for converting lignocellulosic biomass to biofuels.

Justin Lee, currently a graduate student at MIT studying Health Sciences and Technology, is spending the summer at the ALS through the DOE Computational Science Graduate Fellowship program. Lee is working on improvements to the interface with NERSC for beamline scientists.

SF State undergraduate mechanical engineering student Aaron Treger has been doing a summer internship at Beamlines 8.3.2 and 12.2.2, designing different brackets and fixtures to support experiments using 3D modeling. Treger says he’s enjoyed being at the ALS and seeing all the experimental setups.

 

 
NUFO Science Exhibition on Capitol Hill Draws Congressmen, Crowds Print

At the invitation of the House Science and National Labs Caucus, the National User Facility Organization (NUFO) organized a science exhibition to highlight and demonstrate the work done at national user facilities. Held June 26 at the Rayburn House office building on Capitol Hill in Washington, D.C., the exhibition included a number of live demonstrations, videos, and posters in line with its theme, "Energy, Health, and Innovation." It was open to all congressional and senate staff and representatives, as well as the public. All the attendees were excited to learn about user facilities via live science demonstrations. Seven congressional representatives took the time to attend, and over 130 business cards were collected from attendees. ALS representatives in attendance were Prof. Andrew McElrone (USDA-ARS, UC Davis) and Dr. Sue Bailey (ALS User Services Group Leader and NUFO steering committee member).

See the flickr album for more photos. (All flickr photos courtesy of David Gilbert.)

In addition to the exhibition, users from Berkeley Lab user facilities visited 10 Californian congressional offices to describe their research, its importance for California, and why user facilities are needed for their work. McElrone explained how his work looks at the effects of drought on grape vine growth, the vines' water requirements, and the potential to enable water conservation--a critical issue in California (the new ALS Beamline 8.3.2 video features this research).

The ALS is always looking for users with good science stories to showcase during congressional visits. Please contact Sue Bailey if you have ideas for future stories, particularly those that demonstrate how research leads to innovations that change lives.

For more information on NUFO, see http://nufo.org.

 
Small Spot, Brighter Beam Print

Do you notice the brighter beam? During the most recent shutdown, all of the corrector magnets were replaced with sextupoles, reducing the horizontal emittance and increasing beam brightness. “This is part of ongoing improvement to keep the ALS on the cutting edge,” says Alastair MacDowell, a beamline scientist on Beamline 12.2.2.

The brightness has increased by a factor of about three in the storage ring. Beamlines on superbend or center-bend magnets will see the most noticeable increase in brightness, but the horizontal beam size and divergence have been substantially reduced at all beamlines. “We are starting to approach the resolution of many beamlines. Therefore, not every beamline will be able to resolve the full improvement,” says Christoph Steier, project leader of the brightness upgrade. Though superbend and center-bend magnet source sizes are reduced by roughly a factor of three, “measured improvements so far range from a factor of 2-2.5,” Steier says. He and MacDowell agree that the beamline optics are likely the limiting factor in resolving the full improvement at the beamlines.

Martin Kunz and Nobumichi Tamura, staff scientists on microdiffraction Beamline 12.3.2, focus all the photons from the beam to a spot size of one micron. This upgrade increases the intensity of the spot by a factor of at least two, enabling data collection in less than half the time. Kunz's measurements (shown above) indicate a 2.9-times decrease in horizontal beam size and a slight increase in vertical beam size.

 
Shutdown 2013 Update Print
Sextupole upgrade

 

The ALS is replacing all of the corrector magnets with sextupoles (48 of them) to allow for tighter horizontal control of the beam, thereby increasing beam brightness. This so-called "lattice upgrade" will also increase beam brightness by concentrating the horizontal emittance.



(Top) ALS Project and Facility Management Group Leader Steve Rossi proudly shows off a newly-installed sextupole magnet. (Center) Christoph Steier and Arnaud Madur discuss challenges encountered during the installation. (Bottom) A corrector magnet that has been removed from the ring. Some sextupole magnets awaiting installation in the Building 15 staging area.

 

Cold head replacement

 

The cooling elements in the three superbend magnets (and one spare) need to be replaced every 18 months or so, a factor that must be considered when setting the ALS shutdown schedule. These "cold heads" cool the 1.5-ton superbends to an operating temperature of 4K, pumping in liquid phase nitrogen and helium. To replace the cold heads, each must first be warmed up to room temperature, which takes about three days if heating is circulated (it would take about 10 days if left to warm on its own). Crews can then remove the old cold head and ship it off to the manufacturer for refurbishing (like a cold head recycling program). The new piece is installed in its place, the magnets are cooled back down to 4K, and power is restored.

 

Clockwise from top left. 1) A superbend magnet. 2) Inside the superbend, the cold head lies just to the right of the lantern. 3) The new cold head ready to be installed. 4) ) A top-down view into the superbend. 5) Denis Calais (left) and Adrian Williams access the cold head through a hole in the roof of the storage ring. 6) Cooling down the superbend magnet is the final step of installation.

 

New klystron power supply

 

As part of the storage ring radio frequency (rf) upgrade, the ALS installed a new high-voltage power supply that will support the use of two new klystrons instead of the single original klystron installed in 1992. Klystrons are used to provide rf cavities with microwaves that "kick" electrons to boost or maintain their speed. The storage ring has two rf cavities, and the next portion of the upgrade will involve installing a switch that allows operation of one or both cavities on either klystron, if necessary, but with normal operation being one klystron per cavity.

 

Sector 7 upgrade

 

Beamline 7 has been disassembled to make way for MAESTRO (nanoARPES) and COSMIC (Coherent Scattering and Microscopy). One major part of this work was to remove the insertion device from this sector. The giant undulator was hoisted out of the storage ring by a 30-ton crane and positioned on a support slab. Eventually, it will be shipped to another light source for use.



(Top row) The insertion device is hoisted out of the storage ring and moved to a staging area by the 60,000 pound-capacity crane. (Bottom row left) Riggers guide the insertion device (ID). (Center) A close-up view of the ID, shows magnets on the top and bottom direct the path of the x-ray light, which runs through a tube at their center. (Far right) The magnets up close.

 

 

As you can see, this 47,000-pound device was one of the original insertion devices used at the ALS, installed in 1993.

Sector 7 will be chicaned and will receive two new insertion devices where there previously was one. MAESTRO will receive a next-generation nanoARPES chamber in addition to the existing µARPES endstation, new optics, and a sample transfer system. Here are some photos of the front end.

 

 

(From left to right) The front end of Sector 7 is also being upgraded and the floor awaits new equipment. Peer into the storage ring through the open door of Sector 7. Empty racks are awaiting new computers.
 
Berkeley Lab Intern Honored in Intel Science Talent Search Print


intel-wangA New York high school student who wrote a research paper based on her work as a Berkeley Lab Chemical Sciences Division intern this past summer has been named one of 300 semifinalists in the 2013 Intel Science Talent Search, the most prestigious and oldest pre-college science competition in the nation. Chloe Wang, a 16-year-old Dobbs Ferry High School student, spent six weeks in the Chemical Sciences Division and at the Advanced Light Source (ALS) preparing experiments for ALS beamtimes for a research project on hydrogen separation membranes. Wang worked closely with Chemical Sciences Division scientists Hendrik Bluhm and Christoph Rameshan.

“They introduced me to lab procedures and showed me how things operate,” says Wang. “The ALS was probably the most interesting part of the Lab that I saw because it’s such a convergence of scientific disciplines and I’d never been anywhere like that before.”

Wang’s winning research paper, “Effects of Water Vapor on Hydrogen Permeation through a Metal Membrane,” selected from more than 1,700 entrants, examined filtering out hydrogen from other gases by passing it through a thin sheet of metal. Her research determined that water vapor has a negative effect on the permeation of hydrogen. Wang says she’s very interested in alternative energy and found it rewarding to contribute to the preparation of ALS investigations on hydrogen separation research.

Wang’s summer research was part of a project that continues at Molecular Environmental Sciences Beamline 11.0.2 using ambient-pressure x-ray photoelectron spectroscopy (XPS). The beamline’s in situ measurement capabilities allow scientists to study liquid/vapor and solid/vapor interfaces under more realistic conditions.

“Chloe’s initial research gave us parameters and ideas about the issues we’d need to address in our subsequent research,” says Bluhm. “She was a wonderfully enthusiastic student to work with and extremely bright.”

 
ALS Scientists Patent Technique To Dramatically Advance Grating-Based Spectroscopy Print


Gratings – optical elements used to separate light in spectroscopy applications – have been in use since the early 19
th century. Developments in the late 19th century led to the manufacture of gratings by highly precise ruling with a diamond onto a metallic surface. Many gratings are still produced today using the same technique. Holographic methods and ion etching are also used, but all of these techniques result in gratings that contain significant imperfections, which limits resolution.

Watch a video about this topic...

However, a new type of ultra-high diffraction grating recently patented by members of the ALS Experimental Systems Group (ESG), working with colleagues from Berkeley Lab’s Center for X-ray Optics, stands to revolutionize the resolution capabilities of soft x-ray spectroscopy. The key to the new technique is the production of a near atomically perfect substrate, using the anisotropic etching of silicon.

Howard Padmore, head of the ALS Experimental Systems Group, talks about the ultra-high diffraction gratings his group recently developed. See a video of Howard and Dmitriy describing their work.

“Essentially, we’ve discovered a way to make atomically perfect gratings,” says Howard Padmore, head of ESG. “We’re able to make them with very high line density and to make them diffract in high orders, all of which gets us hugely improved resolution and throughput.”

The most serious imperfection in traditional gratings is micro- and nano-scale roughness, which in a reflection grating leads to background scattered light. The consequence, which has a large impact on spectroscopy capabilities, is that gratings are largely limited to 2D surface structures. Much higher efficiency and vastly improved resolution can be achieved with 3D periodic gratings, but this requires perfect interfaces and therefore a perfect substrate. The 3D structure is made by deposition of high and low Z alternate layers on the grating substrate, so that imperfections in the substrate are transferred and amplified in subsequent layers. A good 3D grating therefore needs as close to an atomically perfect substrate as possible.

ESG Scientist Dmitriy Voronov at Beamline 6.3.2, where he tests and characterizes the diffraction capabilities of the new gratings he’s developed.

Dmitriy Voronov, an ESG scientist involved in the development of the new grating technique, created the patentable, atomically perfect grating by using a perfectly suited substrate material: silicon. Since silicon etches in alkali solutions roughly 1000 times faster in some directions than others, a crystalline silicon grating can be created by cutting the crystal so that the slow etching direction is a few degrees from the surface plane. Etching a lithographically defined pattern results in fast etching along the <111> planes, leaving a perfect sawtooth pattern in the silicon. The residual defects are at the level of 1 atomic plane. This near perfect substrate allows the growth of the 3D grating to the necessary perfection. The result is improved efficiency over today’s gratings, with an increase in resolution of up to a factor of 20 for similar conditions.

These new gratings can be applied across a wide range of x-ray science applications. One of the most promising of these is resonant inelastic x-ray scattering (RIXS), a spectroscopy technique that measures both the energy and momentum change of a scattered photon. Unlike traditional photoelectron spectroscopy, RIXS gives scientists element-specific data. The current generation of spectrometers doesn’t provide the resolution needed to fully exploit RIXS, but a higher resolution, higher efficiency grating would resolve this.

These cross-sectional images of the ultra-high diffraction gratings patented by the ALS Experimental Systems Group show the unique structure of saw-tooth grooves with atomically smooth facets.

 

“RIXS is one of the biggest things to happen in x-ray science in the past decade; we need to move from the 100 meV resolution of present instruments to the 5 meV scale of photoemission, and this should be possible using these new techniques” says Padmore.

Voronov says that fabrication of x-ray gratings with the classical ruling technique is quite a slow process — it can take weeks or even months to rule the required number of lines. Moreover, the diamond ruling does not provide superior smoothness of the grooves, which is crucial for 3D gratings. The number of lines and high-order diffraction are key to the technique’s effectiveness since they determine the resolution.

“The anisotropic etch technique we use guarantees almost perfect surface finish of the grooves and a slope of groove’s facets, enabling high-order operation of a diffraction grating,” says Voronov.

“The fact that we can rule these gratings with a very high line density and make them diffract efficiently in a high order means we get higher resolving power,” says Padmore.

With a patent in place, Padmore’s hope is that a company sees the technique as a worthwhile investment and begins commercial production. Until then, the implementation of these gratings at the ALS and other similar facilities will depend on funding. The next steps at ALS will be the integration of the gratings in a real spectrometer and the validation of this new approach. After 200 years of research and application, much still remains to be done to perfect the diffraction grating, one of the most useful and widely used instruments in physical science.

 

Publications

Voronov D L, Anderson E H, Gullikson E M, Salmassi F, Warwick T, Yashchuk V V and Padmore H A, Opt. Lett. 37 (2012) 1628

Voronov D L, Gawlitza P, Cambie R, Dhuey S, Gullikson E M, Warwick T, Braun S, Yashchuk V V and H.A. Padmore, JAP 111 (2012) 093521

Voronov D L, Anderson E H, Cambie R, Cabrini S, Dhuey S D, Goray L I, Gullikson E M, Salmassi F, Warwick T, Yashchuk V V and Padmore H A, Opt. Express 19 (2011) 6320

Voronov D L, Ahn M, Anderson E H, Cambie R, Chang Ch-H, Gullikson E M, Heilmann R K, Salmassi F, Schattenburg M L, Warwick T, Yashchuk V V, Zipp L and Padmore H A, Opt. Lett. 35, (2010) 2615

 
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