As long as electrons are bound to an atom, their energy assumes certain fixed values. These energy values depend primarily on the specific atom and are considered the fingerprint of the system. However, if an atom is in the beam of a very powerful laser, the energy levels are affected, and a so-called photon-field-dressed electronic state can be created.
“This method opens up the possibility to assist chemical reactions and make them happen in a desired way without unnecessary side effects,” says lead author Lukas Bruder, a researcher in physics at the University of Freiburg.
Extreme amounts of energy
To disrupt the electrons around an atomic nucleus and create these special quantum states, very large amounts of energy are applied, on the order of tens to hundreds of trillions of watts per square centimetre. With well-tuned laser pulses, such energies are achieved within an unimaginably short time window of just a few trillionths of a second.
The researchers used the free-electron laser FERMI in Trieste, which was able to generate highly intense radiation pulses in the extreme ultraviolet spectrum. This ultraviolet radiation has a wavelength of less than 100 nanometres and is central to manipulating the electronic states of helium atoms.
“To control the energy states through photon-electron coupling, we used laser pulses that scattered or coalesced depending on the scenario. This was done by adjusting the time delay of the different colour components of the laser beam,” says Raimund Feifel, Professor of Physics at the University of Gothenburg and co-author of the study.
Controlling chemical reactions
Using a highly efficient electron spectrometer from the University of Gothenburg, the researchers were able to obtain measurable information that provides detailed pictures of the electronic states in an atom or molecule.
“The technology we have developed opens up a whole new field of research. This includes new opportunities to make experiments with free-electron lasers more efficient and selective, or to gain new insights into fundamental quantum systems that are not accessible with visible radiation. Above all, it may now be possible to develop methods to study or even control chemical reactions with atomic precision,” says Lukas Bruder.
Scentific article in Nature: Strong-field quantum control in the extreme ultraviolet domain using pulse shaping
Contact info: Raimund Feifel, Professor of Atomic and Molecular Physics at the Department of Physics at the University of Gothenburg, Phone: 0708-38 16 89, e-mail: raimund.feifel@physics.gu.se
