Electrons Seen Moving in Real Time for the First Time

An international team of scientists is using ultrashort flashes of laser light to observe directly the movement of an atom's outer electrons for the first time. Through a process called attosecond (as; 10-18 s) absorption spectroscopy, researchers were able to time the oscillations between simultaneously generated quantum states of valence electrons with great precision. These oscillations drive electron motion.

The collaborative effort for this project included teams from the Max Planck Institute of Quantum Optics (MPQ; Garching, Germany), the U.S. Department of Energy's Lawrence Berkeley National Laboratory (Berkeley, CA, USA), and the University of California (UC) at Berkeley (USA). "With a simple system of krypton atoms, we demonstrated, for the first time, that we can measure transient absorption dynamics with attosecond pulses,” said Dr. Stephen Leone of Berkeley Lab's Chemical Sciences Division, who is also a professor of chemistry and physics at UC Berkeley. "This revealed details of a type of electronic motion--coherent superposition--that can control properties in many systems.”

Dr. Leone referenced recent work by the Dr. Graham Fleming group at Berkeley on the vital role of coherent dynamics in photosynthesis as an example of its importance, noting, "The method developed by our team for exploring coherent dynamics has never before been available to researchers. It's truly general and can be applied to attosecond electronic dynamics problems in the physics and chemistry of liquids, solids, biological systems, everything.”

The investigators' demonstration of attosecond absorption spectroscopy began by first ionizing krypton atoms, removing one or more outer valence electrons with pulses of near-infrared laser light that were typically measured on timescales of a few femtoseconds (fs; 10-15 s). Then, with far shorter pulses of extreme ultraviolet light on the 100-attosecond timescale, they were able to measure exactly the effects on the valence electron orbitals. The findings of the groundbreaking measurements performed at MPQ by the Dr. Leone and Dr. Krausz groups and their colleagues are reported in the August 5, 2010, issue of the journal Nature.

Alterations in molecular structures occur on the scale of many femtoseconds, and these frequently have been seen with femtosecond spectroscopy, in which both Dr. Leone and Dr. Krausz are pioneers.

Dr. Zhi-Heng Loh of Dr. Leone's group at Berkeley Lab and UC Berkeley worked with Dr. Eleftherios Goulielmakis of Dr. Krausz's group to perform the experiments at MPQ. By firing a femtosecond pulse of infrared laser light through a chamber filled with krypton gas, atoms in the path of the beam were ionized by the loss of from one to three valence electrons from their outermost shells.

Related Links:
Max Planck Institute of Quantum Optics
Lawrence Berkeley National Laboratory
University of California at Berkeley