LCLS-II ushers in a new era of science

SLAC fires up the world’s most powerful X-ray laser

With up to a million X-ray flashes per second, 8,000 times more than its predecessor, it transforms the ability of scientists to explore atomic-scale, ultrafast phenomena that are key to a broad range of applications, from quantum materials to clean energy technologies and medicine.

The newly upgraded Linac Coherent Light Source (LCLS) X-ray free-electron laser (XFEL) at the Department of Energy’s SLAC National Accelerator Laboratory successfully produced its first X-rays, and researchers around the world are already lined up to kick off an ambitious science program. 

The upgrade, called LCLS-II, creates unparalleled capabilities that will usher in a new era in research with X-rays. Scientists will be able to examine the details of quantum materials with unprecedented resolution to drive new forms of computing and communications; reveal unpredictable and fleeting chemical events to teach us how to create more sustainable industries and clean energy technologies; study how biological molecules carry out life’s functions to develop new types of pharmaceuticals; and study the world on the fastest timescales to open up entirely new fields of scientific investigation. 

“This achievement marks the culmination of over a decade of work,” said LCLS-II Project Director Greg Hays. “It shows that all the different elements of LCLS-II are working in harmony to produce X-ray laser light in an entirely new mode of operation.”  

Reaching “first light” is the result of a series of key milestones that started in 2010 with the vision of upgrading the original LCLS and blossomed into a multi-year ($1.1 billion) upgrade project involving thousands of scientists, engineers, and technicians across DOE, as well as numerous institutional partners. 

“For more than 60 years, SLAC has built and operated powerful tools that help scientists answer fundamental questions about the world around us. This milestone ensures our leadership in the field of X-ray science and propels us forward to future innovations,” said Stephen Streiffer, SLAC’s interim laboratory director. “It’s all thanks to the amazing efforts of all parts of our laboratory in collaboration with the wider project team.”

Read more on the SLAC website

Image: The newly upgraded Linac Coherent Light Source (LCLS) X-ray free-electron laser (XFEL) at the Department of Energy’s SLAC National Accelerator Laboratory successfully produced its first X-rays. The upgrade, called LCLS-II, creates unparalleled capabilities that will usher in a new era in research with X-rays.

Credit: Greg Stewart/SLAC National Accelerator Laboratory

Polarization shaping of ultrashort extreme-ultraviolet light pulses

Conventional lasers produce light with a well-defined, time-independent polarization. Two common examples are linear polarization, where the electric field oscillates in a certain direction in the plane perpendicular to the direction of light propagation, and circular polarization, where the electric field rotates clockwise (right circular) or counter-clockwise (left circular) about the propagation direction. Recently, however, the generation of pulsed laser light whose polarization is varying on a femtosecond timescale, has attracted significant attention. Such polarization-shaped pulses have been used in a number of applications ranging from manipulation of electron wave packets to improving the sensitivity of advanced spectroscopic techniques.

In the visible, a time-dependent polarization is accomplished using a pulse shaper. On the other hand, lack of efficient optical elements and greater difficulties in controlling the propagation of light at short wavelengths significantly restrain pulse shaping in the extreme ultraviolet (XUV) and x-ray spectral regions. We show here that the externally seeded free-electron laser (FEL) FERMI provides a solution to the problem of tailoring the polarization profile of short and intense XUV pulses.

Read more on the Elettra website

Image: Figure 1 (c & d – click link above to view full figure): The scheme for generating an XUV FEL pulse with time-dependent polarization by combining two counter-rotating FEL sub-pulses. (b) Schematic output of the setup shown in (a) for a separation between the sub-pulse envelopes equal to their FWHM durations (60 fs) and a relative phase (set by PS before R2 in (a)) equal to π/4. Top: components of the total electric field and total intensity. The FEL wavelength is exaggerated to visualize oscillations of the fields. Bottom: temporal profiles of the intensity-normalized Stokes parameters. (c) VMI images obtained from photoionization of helium atoms for a zero delay between the sub-pulse envelopes as a function of the relative phase: the polarization varies from almost pure horizontal (phase = 0, left), to diagonal (phase = π /2, middle), to almost pure vertical (phase = π, right). (d) Intensity-normalized, time-integrated Stokes parameter S1 as a function of the relative phase for zero (left) and 30 fs (right) delay between the sub-pulse envelopes.

Tender X-rays show how one of nature’s strongest bonds breaks

Short flashes of an unusual kind of X-ray light at SwissFEL and SLS bring scientists closer to developing better catalysts to transform the greenhouse gas methane into a less harmful chemical. The result, published in the journal Science, reveals for the first time how carbon-hydrogen bonds of alkanes break and how the catalyst works in this reaction.

Methane, one of the most potent greenhouse gases, is being released into the atmosphere at an increasing rate by livestock farming as well as the continuing unfreezing of permafrost. Transforming methane and longer-chain alkanes into less harmful and in fact useful chemicals would remove the associated threats, and in turn make available a huge feedstock for the chemical industry. However, transforming methane necessitates as a first step the breaking of a C-H bond, one of the strongest chemical linkages in nature.

Forty years ago, molecular metal catalysts were discovered that can easily split C-H bonds. The only thing found to be necessary was a short flash of visible light to “switch on” the catalyst and – bafflingly – the strong C-H bonds of alkanes passing nearby were easily broken almost without using any energy. Despite the importance of this so-called C-H activation reaction, it has remained unknown how that catalyst performs this function. Now, experiments at Swiss FEL and SLS have enabled a research team led by scientists at Uppsala University to directly watch the catalyst at work and reveal how it breaks the C-H bonds.

Read more on the PSI website

Image: An X-ray flash illuminates a molecule

Credit: University of Uppsala / Raphael Jay

Bright Expectations early career event – recording now available!

International Day of Light Early Career Virtual Session

Bright Expectations: Panel discussion with scientists working at 4th Generation Light Sources
Tuesday 16th May 2023

Our Bright Expectations early career event provides an opportunity for viewers to learn what it is like to work at a 4th generation light source directly from scientists from around the world. This interactive session includes short talks from the panellists on the facility they work at/use and their current roles. Ashley White, our moderator, then poses questions to the panel on their career journeys, their views on the advantages and potential of 4th generation lights sources, potential breakthroughs on the horizon and more…

Huge thanks to our amazing panel and moderator!

You can view the recording of the session here

New imaging technique could shed light on individual molecules

An international research team has succeeded for the first time in using X-rays for an imaging technique that exploits a particular quantum property of light. The research team, led by Henry Chapman, leading scientist at DESY and professor at Universität Hamburg, used very intense X-ray pulses from the European XFEL to generate fluorescence from copper atoms. By measuring two photons from the emitted fluorescence almost simultaneously, scientists can obtain images of the copper atoms. The research, published in Physical Review Letters, could enable imaging of individual large molecules.

The atomic structures of materials and large molecules such as proteins are usually determined using X-ray crystallography, which relies on “coherent” X-ray scattering. Undesirable incoherent processes like fluorescence emission, however, can dominate the measurements, adding a featureless fog or background to the measured data. In the 1950s, astronomers Robert Hanbury Brown and Richard Twiss coined a method called “intensity interferometry”, that can extract structural information through the ‘incoherent’ fog. The method exploits the quantum mechanical properties of light, and opened the door to new understanding of light.

Read more on the European XFEL website

Image: The sum of over 58 million correlations of X-ray fluorescence snapshots is shown in the left insert, which was analysed by methods of coherent diffractive imaging to produce a high-resolution image of the source – here two illuminated spots in a spinning copper disk. Right insert: Reconstructed fluorescence emitter distribution at the copper disc with the two beam spots clearly visible.

Credit: DESY, Fabian Trost

That 1st light source experiment: The best way to understand is to experience!

Sae Hwan Chun, beamline scientist and condensed matter physicist at the PAL XFEL

Sae Hwan Chun is a beamline scientist and condensed matter physicist at the PAL XFEL is South Korea, one of the seven XFEL facilities in the collaboration. Sae Hwan is able to research ultra-fast and dynamic phenomena in condensed matter by using the femtosecond X-ray pulses that XFELs generate.

In his #LightSourceSelfie, recalling his first synchrotron experiment at the Advanced Photon Source (APS), Sae Hwan said, “I thought that I understood how to do the experiment, but actually doing it was a completely different matter. It was like even though you pass a written exam for a driving license your mind goes blind to when you actually drive a car for the first time. This first day gave me a lesson that you should experience something if you want to understand it.”