Oldenburg Physicists Reach Record-Stable Laser Pulses for Electron Control

Researchers at Germany's University of Oldenburg have built a laser system that fires 200,000 pulses of light per second while keeping each pulse almost identical to the last, a stability record that could open the door to controlling individual electrons with light. The work, led by Dr. Jan Vogelsang's Attosecond Microscopy research group, is described in a new paper in Applied Physics B — Lasers and Optics.

The team, working with physics Nobel laureate Anne L'Huillier's group at Lund University in Sweden, focused on a property called the carrier-envelope phase (CEP), which fixes the exact position of the peaks and troughs in a light pulse's electromagnetic wave. "You can think of the pulse as a brief flash during which there is room for only a few peaks and troughs," said lead author Katrin Meier, a doctoral candidate at Oldenburg. "The CEP determines where these peaks and troughs are located within the flash." Without a stable CEP, she said, each pulse would differ from the next, making it impossible to run controlled experiments that rely on the fields inside a single pulse.

Using infrared light invisible to the human eye, the researchers kept the CEP stable across timescales ranging from microseconds to several hours, a level of consistency that Meier said surprised the team, given that the CEP is extremely sensitive to temperature changes, air movement and even minor vibrations. To achieve it, the group assembled roughly 100 mirrors and other optical components into a custom laser setup inside Oldenburg's attosecond laboratory.

A small shift in the CEP can strongly influence how electrons react to a laser pulse, Meier said, comparing it to a precisely timed push that determines which way a swing moves. The stability achieved with the new setup allows experiments on electron control that had previously produced no measurable signal at all.