Atomic X-Ray Free-Electron Laser Lights Up for the First Time With an Upgrade That Can Fire Million Pulses per Second

The SLAC National Accelerator Laboratory of the U.S. Department of Energy (DOE) has fired the first X-ray using the upgraded Linac Coherent Light Source (LCLS) X-ray free-electron laser (XFEL).

What is LCLS?

The Linac Coherent Light Source is the world's first hard X-ray-free electron laser facility that can produce X-rays that are very intense and clumped into ultrafast pulses. It became operational in June 2010, serving as a milestone for X-ray user facilities that advance from storage-ring-based third-generation synchrotron light sources to a Linac-based light source.

The LCLS provides laser-like radiation in the X-ray region of the spectrum, providing peak power and peak brightness that is 10 billion times greater than any existing coherent X-ray light source. The SLAC linac produces high-current, low-emittance 5-15 GeV electron bunches at a repetition rate of 120 Hz.

Unlike conventional lasers, the LCLS is a free-electron laser (FEL). It creates light using high-energy electrons that travel in a vacuum through undulator magnets that drive electrons back and forth. The electrons are then produced and accelerated using the final third of SLAC's two-mile linear accelerator.

The LCLS enables scientists to capture images of atoms and molecules in action at a femtosecond scale through its ultra-bright, ultrafast pulses. The scientists are also provided with a unique tool for investigating the arrangement and motion of atoms and electrons in biological molecules, polymers, semiconductors, metals, catalysts, and plastics. This capability of LCLS has the potential to significantly affect the advancement of energy research and other fields of scientific research.

LCLS-II: The Upgraded Free-Electron Laser

Even as X-rays have become a handy tool in healthcare for several decades, scientists continue searching for much more powerful versions that can better probe materials and biological agents. The original LCLS can accelerate electrons through a room-temperature copper pipe, limiting its capability to 120 X-ray pulses per second.

After almost a decade of research, the LCLS Collaboration has announced the "first light" for its upgraded machine, dubbed LCLS-II. By the time it gets fully up and running, LCLS-II is expected to fire a million pulses per second, making it the most powerful X-ray laser in the world. Each pulse can be up to 10,000 brighter than those emitted by previous laser instruments, meaning the upgraded version can be 8,000 more powerful than its predecessor.

The wavelength of the X-ray pulses is about the size of a single atom, allowing the laser to track the internal structure of a molecule. Since it arrives in an ultrafast burst, scientists can 'freeze frame' the motion like a strobe light in a disco.

The LCLS-II produces hard and soft X-rays with high and low wavelengths. The soft X-rays can be used in determining the location of electrons in a molecule, while X-rays can be utilized in visualizing the atomic structure of a material.

Experts will start experimenting using the instrument in the next few weeks, while other scientists can submit proposals for time using the laser. According to DOE Office of Science Director Asmeret Asefaw Berhe, the LCLS-II can be used in fundamental science research in biology, chemistry, and materials and applying scientific advances for clean energy. It can also ensure national security through initiatives such as quantum information science.