Scientists Move Closer to Controlling Individual Electrons

German researchers have developed a highly stable laser system that could bring scientists closer to controlling individual electrons with precisely timed flashes of light. The system, created and tested by physicists at the University of Oldenburg in collaboration with researchers at Lund University in Sweden, produces 200,000 infrared laser pulses every second. According to the team, the pulses are remarkably similar to one another, maintaining a level of consistency that could make previously impossible experiments in ultrafast physics achievable. The work focuses on controlling the electric field of light itself, rather than simply using light as a source of illumination.

The research was carried out by the Attosecond Microscopy group at the University of Oldenburg’s Institute of Physics, led by Dr Jan Vogelsang. The team worked with scientists from a research group headed by Nobel Prize-winning physicist Professor Anne L’Huillier at Lund University. Their results, published in Applied Physics B – Lasers and Optics, describe the detailed characterization of a laser system based on a 200-kilohertz optical parametric amplifier. The system generates pulses with a central wavelength of approximately two micrometres, placing them in the infrared region of the electromagnetic spectrum, beyond the range visible to human eyes.

What makes the achievement significant is not only the high repetition rate but also the extraordinary similarity between successive pulses. Each laser pulse lasts for an extremely short time, containing only a few oscillations of the electromagnetic field. In conventional light sources, small fluctuations can alter the precise shape and timing of those oscillations from one pulse to the next. For experiments that attempt to influence electron motion on attosecond timescales—billionths of a billionth of a second—even tiny variations can obscure the result. The Oldenburg team has now shown that the system can preserve the phase of the light field with exceptional reliability across timescales ranging from microseconds to several hours.

The crucial parameter is known as the carrier-envelope phase, or CEP. A laser pulse can be imagined as a short envelope containing a rapidly oscillating electromagnetic wave. The envelope describes the overall flash, while the carrier is the wave moving inside it. The CEP specifies the exact position of the wave’s peaks and troughs within the envelope. If the CEP changes, the electric field reaches its maximum strength at a slightly different moment, even when the pulse arrives at the same time overall. That difference may appear negligible, but it can determine whether an electron is accelerated, redirected, released from a material or left almost unaffected.

Katrin Meier, a physics doctoral candidate in the Oldenburg research group and lead author of the study, compares the effect to a precisely timed push on a swing. A small change in timing can determine the direction of the swing’s motion. In a similar way, a minimal shift in the carrier-envelope phase can change how an electron responds to an intense laser pulse. This sensitivity is central to strong-field physics, attosecond science and ultrafast spectroscopy, where researchers seek to observe and control the movement of electrons before the surrounding atoms and molecules have time to respond.

Maintaining a stable CEP is one of the most demanding challenges in ultrafast laser science. The phase can be disturbed by temperature changes, air currents, mechanical vibrations and other environmental effects that might be imperceptible in everyday life. Even the expansion of a component caused by a small temperature fluctuation can alter the optical path traveled by the laser beam. To overcome these influences, the researchers designed the laser setup with careful attention to mechanical stability, thermal control and optical alignment. The exceptionally stable conditions in the University of Oldenburg’s attosecond laboratory also played a critical role in keeping the pulses synchronized and nearly identical.

The team was surprised by how stable the CEP remained in the completed experimental arrangement. The researchers examined the laser’s behavior over a broad range of time intervals, allowing them to identify both rapid fluctuations and slower changes that would become visible only after many minutes or hours. This multiscale analysis is important because a laser can appear stable during a brief measurement while drifting over longer periods. By characterizing the system across these different timescales, the researchers demonstrated that the pulse-to-pulse consistency was not a short-lived effect but a durable property of the setup.

The ability to generate such a continuous sequence of stable pulses could transform experiments designed to manipulate electrons directly with light. In many previous measurements, changes in the CEP introduced uncertainty large enough to conceal the signal scientists were trying to detect. If every pulse has a different electric-field waveform, the resulting electron motion becomes an average of many different responses. That makes it difficult to determine whether an observed effect comes from the physical process under investigation or from uncontrolled variations in the laser. With the new system, researchers can repeat the same optical experiment thousands of times while preserving the field conditions that govern the interaction.

This capability could support future investigations into how electrons move through atoms, molecules and solid materials. It may help scientists explore the earliest stages of chemical reactions, examine charge transport in nanoscale systems and improve their understanding of light-driven processes in matter. In the longer term, precise control over electron motion could contribute to technologies such as ultrafast electronic switches and transistors that operate at speeds approaching the natural timescale of light-driven interactions. Such applications remain a future possibility rather than an immediate outcome, but the researchers describe the laser system as an important foundation for experiments that require unprecedented precision.

The study demonstrates that progress in ultrafast science depends not only on producing shorter and more powerful laser pulses, but also on making every pulse reproducible. By stabilizing the carrier-envelope phase of 200,000 infrared pulses per second and tracking its behavior from microseconds to hours, the Oldenburg and Lund teams have created a platform for probing electron dynamics with greater control. Their work turns the subtle waveform of light into an experimental tool, offering scientists a way to deliver repeated, precisely timed pushes to electrons and to study their response at the fastest scales accessible in physics.

News Publication Date: 1 August 2026

Web References: https://doi.org/10.1007/s00340-026-08699-w

References: Applied Physics B

Keywords

Ultrafast lasers, carrier-envelope phase, electron control, attosecond physics, infrared light, optical parametric amplifier, laser stability, University of Oldenburg, Lund University, strong-field physics