Researchers at the University of Oldenburg’s Institute of Physics are working on techniques for precision control of electric fields of light, which allows the dynamics of individual electrons to be manipulated in experiments. Now a team from the Attosecond Microscopy research group, led by Dr Jan Vogelsang, has taken a decisive step towards this goal. 

In the journal „Applied Physics B – Lasers and Optics”, the researchers present a laser system which generates 200,000 light pulses per second. Six Oldenburg researchers collaborated with members of a research group led by physics Nobel Laureate Professor Anne L’Huillier at Lund University (Sweden) to perform a detailed characterisation of the laser system. During the experiments, the precise position of the light wave – consisting of infrared light, which is invisible to the human eye – remained extremely stable even over periods of several hours. The stable light fields resulting from a continuous series of identical light pulses make experiments on electron control possible – foundational research that could eventually lead to the development of devices such as ultra-fast transistors which operate at the speed of light.

The new aspect of this work, as Katrin Meier, lead author of the study explains, is the potentially record-breaking similarity between all 200,000 laser pulses per second. The researchers were able to control the stability of the electric field oscillations across a wide range of timescales, from microseconds to hours. The key factor here is the “carrier-envelope phase” (CEP), which together with other parameters defines the exact shape of the light wave: “You can think of the pulse as a brief flash during which there is room for only a few peaks and troughs in the oscillation of the electromagnetic field. The CEP determines where these peaks and troughs are located within the flash,” says Meier, a doctoral candidate in the research group, which is funded by the German Research Foundation (DFG). “Without a stable CEP, one pulse or flash would be completely different from the next – and controlled experiments that utilise the fields within the pulse would be impossible.”

Because the CEP is extremely sensitive to temperature fluctuations, air movements and even the slightest vibrations, a meticulously planned and executed laser setup, together with the exceptionally stable conditions in the Oldenburg attosecond lab, are essential to its stability. Nevertheless, the stability of the CEP in the current experimental setup took the team by surprise, says Meier. Although the CEP describes only a very small quantity, it can have a major influence on measurement results, she explains: “A minimal shift in the CEP can determine how electrons react to the laser pulse – much like a precisely timed ‘push’ determines the direction in which a swing swings.” The excellent stability of the CEP in the now established setup opens up the possibility to conduct experiments in which it has previously been impossible to record any measurement signals whatsoever.