Tamed light pulses control electrons
GARCHING, Germany – Physicists have controlled the field of white light pulses on a timescale shorter than an optical oscillation, a step forward in light technology and ultrafast photonics that could lead to light-based electronics.
Monitoring the ultrafast motion of the electrons requires ultrashort flashes of light. However, to control them, the structure of these light pulses must be tamed as well. Researchers at the Max Planck Institute of Quantum Optics and Ludwig Maximilians University, led by Eleftherios Goulielmakis and Ferenc Krausz, managed to sculpt waveforms of laser pulses with subcycle precision, making the pulses shorter than a complete light oscillation and thereby creating, for the first time, isolated suboptical-cycle flashes of light.
“We are striving to establish technologies that will permit real-time control of the motion of electrons in their very natural environment,” Goulielmakis said. “But given the inconceivable speed of electron motion (tens to thousands of attoseconds), such control requires the exertion of strong forces that vary very fast. Light fields offer these forces, provided that they are sculpted and controlled with suboptical-cycle resolution.”
To control the light pulses on a subcycle timescale, it was necessary to use white laser light because it contains wavelengths ranging from the near-ultraviolet to near-infrared. The physicists created these light pulses and sent them into a newly developed light field synthesizer that superimposes optical waves of different colors and phases to create various field shapes. The device first splits the incident white laser light into red, yellow and blue color channels. After manipulating the properties of the individual colors, itrecombines them to form the synthesized waveform.
A light field synthesizer divides incident white light into three color channels and modifies it afterward. The composition creates laser pulses with a complex, however fine, adjustable waveform. Courtesy of Thorsten Naeser.
Using this technology, the scientists generated completely new isolated waveforms and, in so doing, achieved the shortest pulses ever measured in the visible spectral range – 2.1 fs. These pulses are more intense than the ones commonly produced by current femtosecond light sources because all the energy of the electromagnetic field is confined into a tiny temporal window.
It is precisely these powerful and specially tailored electromagnetic forces that are necessary to control electrons in atoms and molecules, as they are similar in strength to the forces occurring in such microscopic systems. However, to steer electron motion on a microscopic scale, another prerequisite is precision. This desired level of precision is provided by the well-controlled waveforms of the synthesized light pulses.
The research appeared online Sept. 8 in Science (doi: 10.1126/science.1210268).
The physicists have already applied their novel technique in an experiment. When the newly designed light pulses were shone onto krypton atoms, the outermost electron was ripped away within less than 700 attoseconds, marking the fastest electronic process that has been initiated by visible light.
“We expect exciting applications in several thematic areas of modern ultrafast science,” Goulielmakis said. “We anticipate new ways to influence the result of chemical reactions in real time or in solids to drive electronic currents with light fields.”
The team aims to extend the spectral bandwidth supported by the synthesizer even further toward the deep-ultraviolet and infrared parts of the spectrum. This will offer even higher resolution for controlling and sculpting light fields, he said.
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