X-ray pulses – Lightsources.org

Lasing achieved with hard X-rays in a resonator

2026/01/282026/01/29

Novel “XFELO” laser system produces razor-sharp X-ray light

For the first time, researchers have amplified X-ray light multiple times in a resonator cavity, in a way highly similar to traditional lasers. With great success: the new technique delivers extremely energetic X-ray pulses for high-precision experiments. This development opens up entirely new possibilities for research in physics, chemistry, or biology. The system is called “XFELO”. Researchers from European XFEL, DESY and Hamburg University have published their findings in the latest edition of the journal Nature.

The team of engineers and scientists have shown for the first time that a hard-X-ray cavity can provide net X-ray gain, with X-ray pulses being circulated between crystal mirrors and amplified in the process, much like happens with an optical laser. The result of the proof-of-concept at European XFEL is a particularly coherent, laser-like light of a quality that is unprecedented in the hard X-ray spectrum. Lasing inside a cavity had been challenging to achieve with short-wavelength X-rays for a variety of reasons, including – on a basic level – that the nature of the light makes it difficult to reflect the beam at large angles. The “XFELO” (short for: X-Ray Free-Electron Laser Oscillator) technique opens new perspectives for scientific investigations, from ultrafast chemical reactions to detailed analyses of the smallest biological structures.

Read more on the European XFEL website

Image: Illustration of the XFELO system: a hard X-ray pulse (red) is reflected by a set of diamond mirrors and oscillates through arrays of magnets, so called undulators. On each roundtrip the pulse meets a new electron bunch (blue), which emits X-rays while passing through the undulators on a slalom course.

Credit: European XFEL

World record attosecond measurement at SwissFEL

2025/05/062025/05/16

As scientists push X-ray free electron lasers into the attosecond regime, diagnostic tools with higher precision are needed. Now scientists at the Paul Scherrer Institute PSI have demonstrated the ability to characterise pulses as short as 300 attoseconds: a world record time-resolution using electron-beam streaking.

X-ray free electron lasers such as SwissFEL generate short and powerful pulses of X-ray light that allow scientists to study atomic and molecular processes in action. Scientists are now striving to generate shorter and shorter pulses to access attosecond timescales (10^-18 s) and observe the motion of electrons in real time.

Capturing such ultrafast processes with X-rays requires not only attosecond pulses; it also requires ways to precisely characterise the X-rays. “You need to know exactly how long each pulse lasts for and when the brightest parts of the pulse hit, for example,” says Eduard Prat, scientist in the beam dynamics group at SwissFEL. “For many scientific applications, if you don’t have this information, you’re blind.”

A team from PSI has recently demonstrated that the PolariX – a type of radiofrequency deflector device developed by PSI in collaboration with CERN and the German research centre DESY – can meet the ambitious requirements of attosecond science.

The electrons tell the story of the X-rays they made.

To create the X-ray light in the SwissFEL, bunches of electrons are accelerated to close to the speed of light and wiggled in a series of magnets called undulators, whereby they emit intense bursts of photons – the X-ray pulses.

At attosecond timescales, it’s difficult to measure the properties of these pulse directly in a reliable way. X-rays interact only weakly with matter, and traditional sensors aren’t fast enough to resolve attosecond-scale events. Instead, scientists can study the electrons that produced them.

Sitting after the undulators, the PolariX measures the electron bunch after they’ve released their photons. The device bends the beam using a radiofrequency field, spreading out the electrons depending on their exact arrival time – a method known as electron beam streaking. From the spread, the length of each individual electron bunch can be measured.

When the electrons emit photons (in technical terms, they ‘lase’), they lose energy. By measuring this energy difference, and how it is spread at the parts of the electron beam that lase, PolariX provides information on the X-ray pulse, in particular how its intensity varies over time.

A #MadeAtPSI success story

Although electron streaking is a relatively well-established technique for X-ray pulse characterisation, what makes PolariX unusual is that it can streak in any direction, helping to fully characterise the electron bunch – a concept invented at CERN and realised thanks to the radiofrequency technology at PSI. In contrast, most other devices only streak in one direction, giving limited information about the electron beam.

During the last seven years of development at PSI, the PolariX has become one of the world leading devices for this purpose. Five devices are in operation at DESY in Germany, with whom the device was developed, and the team at PSI is currently in discussion with other institutes worldwide to provide them with their RF technologies.

“Pretty much all of the systems and components of PolariX were made at PSI,” says Paolo Craievich, who leads the RF systems group at PSI. “Over the course of PolariX’s development, we have become very experienced, and now we are leading in the world. I’m very proud for the whole RF section – it’s the work from many different people.”

Read more on PSI website

Image: Eduard Prat (left) and Paolo Craievich in SwissFEL – proud of the teamwork that has now led to a world record time-resolution in X-ray pulse measurement using electron-beam streaking. © Paul Scherrer Institute PSI/Mahir Dzambegovic

Credit: Paul Scherrer Institute PSI/Mahir Dzambegovic

New imaging technique could shed light on individual molecules

2023/04/252023/04/26

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.

Superconducting X-ray laser reaches operating temperature colder than outer space

2022/05/102022/05/11

The facility, LCLS-II, will soon sharpen our view of how nature works on ultrasmall, ultrafast scales, impacting everything from quantum devices to clean energy.

Nestled 30 feet underground in Menlo Park, California, a half-mile-long stretch of tunnel is now colder than most of the universe. It houses a new superconducting particle accelerator, part of an upgrade project to the Linac Coherent Light Source (LCLS) X-ray free-electron laser at the Department of Energy’s SLAC National Accelerator Laboratory.

Crews have successfully cooled the accelerator to minus 456 degrees Fahrenheit – or 2 kelvins – a temperature at which it becomes superconducting and can boost electrons to high energies with nearly zero energy lost in the process. It is one of the last milestones before LCLS-II will produce X-ray pulses that are 10,000 times brighter, on average, than those of LCLS and that arrive up to a million times per second – a world record for today’s most powerful X-ray light sources.

“In just a few hours, LCLS-II will produce more X-ray pulses than the current laser has generated in its entire lifetime,” says Mike Dunne, director of LCLS. “Data that once might have taken months to collect could be produced in minutes. It will take X-ray science to the next level, paving the way for a whole new range of studies and advancing our ability to develop revolutionary technologies to address some of the most profound challenges facing our society.”

With these new capabilities, scientists can examine the details of complex materials with unprecedented resolution to drive new forms of computing and communications; reveal rare 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 peek into the bizarre world of quantum mechanics by directly measuring the motions of individual atoms.

A chilling feat

LCLS, the world’s first hard X-ray free-electron laser (XFEL), produced its first light in April 2009, generating X-ray pulses a billion times brighter than anything that had come before. It accelerates electrons through a copper pipe at room temperature, which limits its rate to 120 X-ray pulses per second.

Read more on the SLAC website