Powerful Lasers in Prague
XFELs celebrated at SPIE Optics + Optoelectronics.
The European X-ray Free Electron Laser (XFEL) in Germany was the subject of much celebration during and shortly after SPIE Optics + Optoelectronics this spring.
European XFEL Managing Director Robert Feidenhans’l, one of five plenary speakers at the SPIE conference in Prague in April, announced on 4 May that the biggest X-ray laser in the world had generated its first X-ray laser light.
“The facility, to which many countries around the world contributed know-how and components, has passed its first big test with flying colors,” Feidenhans’l said, adding that his colleagues and international partners “accomplished outstanding work.”
The 3.4 km long facility, most of which is located in underground tunnels near Hamburg, has the most powerful linear accelerator in the world and marks the beginning of a new era of research in Europe. The German research center DESY, the largest shareholder of the European XFEL, put the accelerator into operation at the end of April.
It has an X-ray light with a wavelength of 0.8 nm — about 500 times shorter than that of visible light. At its first lasing, the laser had a repetition rate of one pulse per second, which will later increase to 27,000 per second.
Feidenhans’l reported at SPIE Optics + Optoelectronics that once the facility is fully operational, the system will provide a peak brilliance billions of times higher than that of conventional X-ray sources, with photon energies in the range of 0.3-24keV and pulse widths on the order of 10-100fs.
The European XFEL will enable applications development in the areas of structural dynamics, nanoscale imaging, and non-linear X-ray science, he said.
“We can now begin to direct the X-ray flashes with special mirrors through the last tunnel section into the experiment hall, and then step by step start the commissioning of the experiment stations,” he said. “I very much look forward to the start of international user operation, which is planned for September.”
Since the achievable laser light wavelength corresponds to the size of an atom, the X-rays can be used to make pictures and films of the nanocosmos at atomic resolution, such as of biomolecules, from which better understandings of the basis of illnesses or the development of new therapies could be developed. Other opportunities include research into chemical processes and catalytic techniques, with the goal of improving their efficiency or making them more environmentally friendly.
With more than 27,000 light flashes per second instead of the previous maximum of 120 per second, an extremely high luminosity, and the parallel operation of several experiment stations, scientists will be able to investigate more limited samples and perform their experiments more quickly. The new facility means an increase in the amount of “beamtime” available to scientists, as the capacity at the other four X-ray lasers worldwide has been eclipsed by demand, and facilities have been overbooked.
Several conferences at SPIE Optics + Optoelectronics were devoted to XFEL applications, sources, damage, and instrumentation.
In a conference on sources and instrumentation for XFELs later in the week, Sebastien Berujon of the European Synchrotron Radiation Facility (France) discussed the development of a hard X-ray wavefront sensor for use in the European XFEL beamline.
Criteria for the sensor include beam wavefront characterization for each pulse in a non-invasive fashion.
A challenging aspect of the design results from the fact that within the 10Hz-repetition-rate pulse train lies individual pulses within each burst at a 4.5MHz repetition rate. Characterizing each of those pulses requires fast optical components.
Several approaches to at-wavelength metrology exist, and the team adopted a new approach leveraging near-field speckle properties, Berujon said. The resulting setup relies on two streaming cameras and low-absorbing, fast-decay-time scintillators to image the beam with minimal disturbance.
Particularly impressive was the implementation of an X-ray speckle scanning mode capable of reaching single nano-radian accuracy.
Plenary talks during the week encompassed the range of technology and science showcased at SPIE Optics and Optoelectronics.
Jonathan Zuegel of the Laboratory for Laser Energetics at University of Rochester (USA) described work being done to produce scalable technologies to upgrade the OMEGA EP laser system to enable pumping of the EP OPAL optical parametric amplifier line. The end goal is an output power density in excess of 1023W/cm2 with pulse widths of approximately 20fs.
Primary challenges included development of appropriately sized broadband gratings with suitable damage threshold and ultrabroadband wavefront control and focusing to achieve the desired intensities.
Constantin Haefner of the US National Ignition Facility and the Photon Science Directorate at Lawrence Livermore National Lab (LLNL) discussed the development of high-repetition-rate petawatt lasers and in particular the High-repetition-rate Advanced Petawatt Laser System (HAPLS).
LLNL developed HAPLS in conjunction with the Extreme Light Infrastructure (ELI) beamlines team with the goal of installing the system at ELI-Beamlines in the Czech Republic in 2017. It represents a significant step forward in taking high-power systems towards higher repetition rates in anticipation of eventually moving towards commercial applications.
The system produces 1PW at 10Hz as demonstrated during its commissioning run in late 2016. Measuring 17m x 4.6m, the tabletop system takes advantage of eight core technologies including gas cooling for the amplifiers and high-average-power gratings to meet specifications.
SPIE Fellow Kishan Dholakia of the University of St Andrews (UK) discussed utilizing the forces resulting from the scattering of light from and refraction of light through micron-sized objects to manipulate such objects.
Optical manipulation of materials not only encompasses interesting physics but has found a variety of applications, particularly in the life sciences.
Dholakia described how the slow-light effect in photonic crystal waveguides enhances the speed with which one can move objects. He discussed not only translational motion of objects but also how to utilize circularly polarized light to effect rotation and the benefits in Q-factor seen when operating in a vacuum, which has implications in sensing applications.
Although this method has been around for over 40 years, Dholakia’s presentation showed that future applications in sensing and in conducting tests at the classical-quantum interface as well as other areas will keep it relevant and interesting in the future.
SPIE Fellow Demetri Psaltis of the Ecole Polytechnique Fédérale de Lausanne (Switzerland) gave a plenary talk on imaging with multimode fibers, reporting on promising results that bode well for the future of multimodal fibers in endoscopic applications and in other imaging applications.
The research is motivated by the need for improvements in endoscopes, which currently rely on fiber bundles of millimeter sizes in diameter. Because bending the fibers can be an issue, the system historically has been used as a rigid probe.
Multimode fibers provide a path to reduce these diameters into the hundreds of microns range, albeit with larger core diameters than that found in single-mode fibers. This results in a deterministic scattering and modal dispersion that can be analyzed to produce high-quality images, something that was demonstrated in fluorescent imaging of neuronal cells. The large number of temporal and spatial degrees of freedom available with multimodal fibers enables high-resolution imaging in a compact operation.
Psaltis described recent work on speckle scattering microscopy, which eliminates the need for calibration and demonstrates no bending sensitivity.
Some of the most advanced laser technologies were covered in a workshop on intense, high-average-power lasers and a conference on high-power, high-energy, and high-intensity laser technology, and the week wrapped up with a tour to the HiLASE Laser Centre and ELI Beamlines facility.
Recordings of some of the presentations from SPIE Optics + Optoelectronics 2017 can be found in the SPIE Digital Library along with the proceedings papers.
Read the event news from SPIE Optics + Optoelectronics.
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