Scientists from the Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy (MBI) in Berlin, Germany, in collaboration with international research colleagues in Canada and in Japan, have realized what is known as an attosecond experiment.
The resulting groundbreaking insights into the structure and dynamics of electrons are enabled by the ultrafast — in fact, attosecond — laser pulses. An attosecond is one quintillionth of a second, which compared with a full second roughly correspondents to the relationship between one second and the age of the universe.
“We have conducted an experiment where we have fully characterized the quantum-mechanical wavefunction of an ionized electron,” reports Professor Dr Marc Vrakking, director at BMI. “According to quantum mechanics, electrons are characterized by a number of properties, such as their charge, their energy, their angular momentum — a property that describes the shape of an orbit that an electron is on — and their spin.”
Complete characterization of electrons' angular momentum
In the current experiment, the international team of researchers removed the electrons from neon atoms, leaving the electrons with the possibility to have different magnitudes of the angular momentum. The scientists determined the probabilities for each magnitude of the angular momentum as well as another aspect of the quantum-mechanical theory, namely the relative phase of these angular momentum contributions. Atomic physicists call such complete characterization of the angular momentum of electrons a “complete” or a “perfect” experiment, according to Vrakking, who adds, “Such experiments are rare and often very difficult to perform. Using attosecond laser techniques, however, the experiment became feasible.”
The accomplishment of completely measuring and describing the quantum-mechanical wave function of an ionized electron could bring about a significant leap in laser physics research. “Attosecond science has as its main goal to get a deeper understanding of the role of electrons in defining chemical bonding, material properties, etc.,” Vrakking notes. “The experiment sets a new standard for the detailed description of the properties of electrons in attosecond experiments.”
Attosecond snapshot of moving electron
The professor goes on to explain the importance of attosecond light pulses in nanoscience: “In general, attosecond pulses are relevant since they have a duration that is short enough so that the motion of electrons can be frozen,” he says. “With attosecond pulses, we can take snapshots of the motion of electrons, the way that a high-speed camera can make sharp pictures of fast-moving objects.”
And since the attosecond pulses are so short, they are inevitably accompanied by a large uncertainty in their wavelength/photon energy. “This uncertainty was exploited in the current experiment to perform a series of interference experiments that resemble the well-known double-slit interference for light beams,” Vrakking says. “The interferences allowed us to recognize the probabilities of different angular momentum states, as well as their relative phase.”
The laser research breakthrough could influence the advancement of light-based technologies in the future, the expert agrees. “Having been able to fully characterize electrons in this atomic laser ionization experiment may motivate attempts to fully characterize electrons in other contexts, potentially related to real-life applications like electronics and communication,” he projects.
In the current experiment, Vrakking and his colleagues completely characterized electrons that were ionized, meaning they were kicked out of atoms as a result of their interaction with the lasers. “It would be an exciting goal to try and perform such a characterization of electrons that are bound inside an atom,” he says in conclusion.
The results of this research are detailed in the article “Coherent imaging of an attosecond electron wave packet,” published in the journal Science.
Written by Sandra Henderson, research editor Novus Light Technologies Today.