Atomic X-Ray Laser Opens Door To Attosecond Imaging

A newly discovered X-ray laser approach is fast and powerful enough to capture details about the movement of electrons.

Berkeley Lab’s Molecular Biophysics and Integrated Bioimaging (MBIB) Division scientists were part of the team that has generated the shortest pulses of high-energy X-rays to date by using a powerful laser to stimulate inner shell electrons – the electrons closest to an atomic nucleus. These extremely short pulses, clocking in at 60-100 attoseconds (quintillionths of a second), could be used to study quantum-scale phenomena that occur so quickly they are assumed to be unobservable.

Previous experiments using femtosecond pulses (1,000 times longer than an attosecond) showed electrons as a cloud that surrounds the atom. Uwe Bergmann, a professor at the University of Wisconsin-Madison and an MBIB affiliate researcher, is lead author on a new paper about the process, now published in Nature.

Fundamental theories of quantum mechanics state that it is impossible to pinpoint the location of an electron at a given time. This new attosecond timescale enabled by the team’s laser system will allow researchers to investigate how that electron cloud moves.

“Femtosecond laser pulses let us study atomic bonds breaking and forming,” elaborated co-author Vittal K. Yachandra, an MBIB senior scientist. “Now we’re going inside to look at not just the making or breaking of a bond, but what actually is a bond?”

Bergmann and an international team of colleagues used the two most powerful X-ray lasers in the world – the Linac Coherent Light Source (LCLS) at SLAC National Accelerator Laboratory and the SPring-8 Ångstrӧm Compact free electron LAser (SACLA) in Japan – to excite inner shell electrons in copper and manganese atoms. For years, Bergman, Yachandra, and their MBIB colleagues, senior scientist Jan Florian Kern and Division Director Junko Yano, have been using X-ray lasers at SLAC and SACLA to study metalloenzymes, such as those that drive photosynthesis and respiration, at the atomic level. Over time, the researchers invented a powerful laser system that can produce both extremely short pulses of light and very high-energy light, allowing them to study many properties of molecules and materials.

This inner-shell lasing phenomenon will be studied more deeply and integrated into tools at existing laser facilities so the scientific community can begin exploring the vast potential of attosecond hard X-rays. Co-author Yano said, “It is also intriguing to speculate what unexpected discoveries with this approach might lie ahead, as did so when strong lasing effects were first discovered by the pioneers of laser physics exactly 70 years ago, leading to one of the most powerful and widely used tools in modern technology.”