Physicists at the University of Oldenburg have generated three-dimensional light fields by superimposing intersecting laser pulses in a vacuum chamber. The technique allows researchers to push electrons into higher-energy quantum states previously inaccessible in experiments, opening new pathways for investigating molecular chirality and light-matter interactions.
Using an interferometer, researchers split laser light into two beams of different colors and superimposed them in a vacuum chamber. The method combines two specially shaped femtosecond laser pulses—extremely short bursts of light lasting a few millionths of a billionth of a second—that converge from different directions.
The beams intersect at a single point to create three-dimensional light fields whose shape can be controlled by changing the polarization of the two pulses.
One pulse was redder, centered around 929 nanometers, while the other was bluer, centered around 720 nanometers. When the pulses met at an angle of 45 degrees, their electric fields combined so that the resulting light field oscillated in all three spatial directions, providing a level of control that ordinary planar laser fields cannot achieve.
University of Oldenburg Physicists Excite Potassium Electrons
The research team demonstrated the technique by selectively exciting electrons in potassium atoms into higher-energy excited states before releasing them from the atoms. By simultaneously observing changes in electron states at short intervals, the experimental setup functioned like an ultrahigh-speed camera for quantum processes. The stroboscopic flash lighting technique allowed the team to capture successive stages of different electron states to form a movie of their evolution.
“With our method, we can generate electronic quantum states that have previously only been described theoretically and also make them spatially visible,”
Dr. Matthias Wollenhaupt, who leads the research team
“We have thus expanded the experimental optics toolkit to include a new class of three-dimensional light fields.”
Dr. Matthias Wollenhaupt, who leads the research team
Darius Köhnke, a Ph.D. student in the Ultrafast Coherent Dynamics research group and one of the lead authors of the study, explained that the fields oscillate in all three spatial directions to open new possibilities for investigating and controlling specific light-matter interactions. The findings were reported in the journal Physical Review Research under the title Multiphoton ionization with three-dimensional light fields.
New Method Helps Investigate Chiral Molecules
The new method holds promise for investigating chiral molecules, which play roles in biology and medicine. Chiral molecules exist in two mirror-image forms that cannot be superimposed, comparable to human left and right hands. Many biomolecules—including amino acids, carbohydrates, and active ingredients in medicinal products—are chiral, and their two forms frequently possess different properties. For instance, the active ingredient thalidomide in the medication Contergan has one form that causes birth defects during pregnancy and another that is harmless, though separating the two forms is difficult.
Because theoretical studies show that three-dimensional light fields can possess chiral properties, the technique could advance the field of chiral sensing. Olga Smirnova, a physicist at the Max Born Institute for Nonlinear Optics in Berlin, recently highlighted the possibilities of three-dimensional light fields for investigating and controlling molecular chirality in a Science article titled A New Age of Molecular Chirality.
The University of Oldenburg physicists noted that their current study lays a foundation for such applications.