Today, he is group leader and leading scientist for the High Energy Density Science (HED) instrument at the European XFEL, a facility under construction in Germany. HED will be used to conduct studies similar to those Zastrau participated in at SLAC
, looking at "warm dense matter" like that found at the cores of giant planets.
"I gained all the skills I needed to accomplish my current job by helping to build MEC during my fellowship," he says.
Zastrau's bi-continental success strengthens international relationships that will foster cross-fertilization in XFEL science between labs and countries, according to his former mentor Siegfried Glenzer, professor of photon science and director of the new High Energy Density Science division at SLAC.
"Ulf brought new designs and ideas to MEC," Glenzer says. "As a result of our close relationship through the fellowship, the strong collaboration of our HED groups at SLAC and at European XFEL will continue when they switch on their machine in 2017."
The European XFEL is now host to fellow Emma McBride who works with Zastrau's group in Germany and Glenzer's group at LCLS. Her fellowship will continue through 2018.
The fellowship, formally known as “Free-electron Laser Science: Peter Paul Ewald Fellowships at LCLS in Stanford” was created to advance XFEL-related science in the run-up toward the opening of the European XFEL in Hamburg, according to Ulrike Bischler, program director at the Volkswagen Foundation.
It was also designed to help develop the careers of promising young scientists and to support transatlantic exchange and networking. Ewald, who was born in 1888 in Berlin and died in 1985 in Ithaca, New York, was a German crystallographer and physicist who was a pioneer of X-ray diffraction methods.
The five-year program concluded with a last round of accepted proposals in 2015, and those fellows will continue work through 2018. A total of 16 three-year fellowships were awarded starting in 2011, representing an investment of €5.5 million, including support of symposia and FEL summer schools at DESY. The Peter Paul Ewald fellows will hold a workshop at SLAC April 21-22.
The Volkswagen Foundation is an independent, non-profit organization and has funded research projects in all disciplines since 1962.
"The Peter Paul Ewald fellowships are a success story for the foundation," Bischler says. "The scientific environment at SLAC proved to be beneficial for the academic and personal growth of the initially early-career postdocs. Afterwards all fellows decided to continue in academia, now as senior postdocs or group leaders. The funding has resulted in excellent research published in high-level journals, and I am confident that more exciting results will follow from the later fellows who have just started."
Current fellow Christian Roedel has been at SLAC for more than a year working on relativistic laser plasma interactions – research that could have applications in particle acceleration for medical purposes and next generation accelerator technology. His recent experiments have shown that astrophysical scenarios can be studied in the laboratory using these interactions.
After all, successful science using facilities like LCLS relies on a close network of international partners, he says. He likes the fact that fellows can work at SLAC without losing the support system they have built up in Germany. "We can establish the connections and knowledge of working in two countries and take the best approaches from both parts of the world to further the science."
Tais Gorkhover began her fellowship in 2013 in Germany and has since performed experiments at SLAC in pursuit of a novel imaging technique based on holography using X-ray lasers that could greatly simplify the reconstruction of structures revealed at LCLS.
"The fellowship allowed me to initiate an international collaboration, which resulted in a successful proof-of-principle experiment of 'in-flight' holography," she says. "We are wrapping up the data analysis on this first experiment and preparing the first paper draft. In addition, we are preparing follow-up experiments at LCLS and FLASH at DESY with the aim to advance the method."
Gorkhover, who's fellowship will end in 2017, also led a study on time-resolved imaging of single superheated nano-samples that was published recently in Nature Photonics
. Support of her mentor, former LCLS researcher Christoph Bostedt, who is now at Argonne National Laboratory and Northwestern University, was crucial to the positive outcome of her fellowship, she said.
Fellowship program advisor Keith Hodgson, professor of chemistry at Stanford and of photon science at SLAC, emphasizes the historical significance of SLAC and DESY partnerships that these fellowships continue. Collaboration with Germany has been key since the early development of the LCLS instruments, he points out, and X-ray free-electron lasers have since generated much global collaboration.
"The XFEL scientific community is engaged from all regions of the world; it is complex and requires large collaborations," he says. "Scientists around the world are trying to answer similar questions. The innovative Ewald Fellows Program sponsored by the Volkswagen Foundation is a tremendous magnet to bring talented young researchers into this exciting field and mentor them for launching their own independent research careers."
Fellowship mentor David Reis, PULSE researcher and associate professor of photon science and applied physics at SLAC and Stanford, emphasizes the benefit of this international program to the lab. "It's an excellent opportunity for us to bring in new people and let them explore their ideas," he says. "It allows us to branch into directions we may otherwise not pursue."
Matthias Fuchs, one of the first fellows Reis mentored, went on to become assistant professor of physics and astronomy at the University of Nebraska. While he was at SLAC he explored "nonlinear" X-ray behavior that can only be seen at XFELs. A publication of his work
in Nature Physics
last year was the beginning of studies that could have significant impact on future experiments performed with high-intensity X-rays.
"The fellowship gave me the freedom to investigate what many people considered a rather crazy idea," Fuchs says, "but it has led to some really exciting and unexpected results."
Like many of the fellows, Fuchs performed research that could only be done at LCLS, benefiting the future of XFEL science while building a bright future for his career as a scientist.