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With the help of the generation of the first optical attosecond pulses, scientists from the Laboratory for Attosecond Physics determined the length of time that electrons in atoms need to react to the electromagnetic forces of light.
In the race for ever faster electronics, light could play an important role. For example, physicists pursue the goal of controlling electrical currents in circuits with light frequencies with short light pulses of a precisely controlled waveform. But will the electrons in the circuits immediately follow the light oscillations? How quickly will you react to pressing a "light-based" button? Or, as a fundamental question: how quickly do electrons, which are bound in atoms, molecules or solids, respond to the irradiation of light? Now an international team of scientists led by Dr. Eleftherios Goulielmakis, head of the “Attoelectronics” research group at the Max Planck Institute for Quantum Optics, together with researchers from Texas A&M University (USA) and the Lomonossow State University in Moscow (Russia) measured such a delay effect for the first time. In doing so, they excited krypton atoms with optical attosecond light pulses and observed that it takes around 100 atto seconds for the electrons to react to the electromagnetic forces of light.
According to the predictions of quantum mechanics, even the lightest particles outside the atomic nucleus, the electrons, need a certain, albeit very short period of time to react to the forces of light. It only takes a few 10 or 100 attoseconds (1 as is a billionth of a billionth of a second), which is why this process was previously considered immeasurably fast.
"A prerequisite for capturing such a brief event is a flash of light that sets the electrons in motion extremely quickly - in technical jargon" polarizes "- and thus tests their reaction time," explains Dr. Mohammed Hassan from the research group of Dr. Goulielmakis. The scientists produce such a flash of light with a so-called “light-field synthesizer”. In doing so, they manipulate the properties of visible, near-infrared and ultraviolet light in such a way that they can then compose a light pulse in the visible range with a length of only 380 attoseconds. The pulses are so short that they hardly carry more than half an oscillation of the light field with them and are therefore the shortest pulses ever generated in the visible range. "We can not only manipulate visible light with attosecond precision, but also limit its waves to attosecond time intervals," explains Dr. Tran Trung Luu, scientist in Dr. Gouliemakis.
With this new tool, the scientists had a method to excite krypton atoms with optical attosecond pulses. By varying the intensity and phase of the respective pulses, they achieved that slightly different forces acted on the electrons in the atoms in different experiments. Using the vacuum ultraviolet radiation emitted by the electrons, they could see how the electrons react to it. From this they could deduce that it takes about 100 attoseconds for the electrons to respond to the power of light.
“Our study puts an end to the decades-long debate about the fundamental dynamics of light-matter interaction. In the last few decades we have already been able to uncover both the rotational movements and the nuclear movements in molecules with femtosecond technology. Now, for the first time, we can also follow the reaction of the electrons bound in the atoms in real time, ”emphasizes Dr. Goulielmakis. "But at the same time we are at the beginning of a new era in which we will examine and manipulate matter by influencing electrons."
One of the next steps that Goulielmakis and his team are planning is to extend these investigations to include electron dynamics in solids. “This will enable us to find out the best way to implement innovative, ultra-fast electronics and photonics that work on time scales of a few femtoseconds and with Petahertz clock frequencies,” explains Goulielmakis.
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