Physicists at the University of Oldenburg combined two ultrashort laser pulses to generate controllable three-dimensional light fields, reaching previously inaccessible electronic quantum states in potassium atoms. The experimental optics method, published in Physical Review Research, captured successive stages of electron evolution and could advance chiral molecule identification.
Superimposing two specially shaped femtosecond laser pulses converging from different directions allowed researchers to create controllable three-dimensional light fields. The team combined two laser beams of different colors, making their beams intersect at a single point inside a vacuum chamber using an interferometer. These ultrashort bursts of light last just a few millionths of a billionth of a second.
“With our method, we can generate electronic quantum states that have previously only been described theoretically and also make them spatially visible,” Prof. Dr Matthias Wollenhaupt, who leads the research team at the University of Oldenburg, explained in a press release. “We have thus expanded the experimental optics toolkit to include a new class of three-dimensional light fields.”
The fields oscillate in all three spatial directions. This oscillation provides new ways to investigate and control specific light-matter interactions, according to Darius Köhnke, a PhD student in the Ultrafast Coherent Dynamics research group and one of the two lead authors of the study.
Potassium Atom Experiments Capture Successive Stages of Quantum-State Evolution
Researchers demonstrated the procedure by using the generated 3D light field to selectively excite electrons in potassium atoms into higher-energy states—known as excited states—and subsequently release them from the atom. Observing changes in electron states at short intervals allowed the method to function like an ultra-high-speed camera for quantum processes. The stroboscopic flash lighting technique captured successive stages of different electron states, forming a movie of their evolution.
The approach holds particular promise for investigating chiral molecules, which play key roles in biology and medicine. Chiral molecules exist in two non-superimposable mirror-image forms, much like human left and right hands. Many biomolecules, including amino acids, carbohydrates, and active ingredients in medicinal products, are chiral. Their two forms frequently possess different properties.
For example, the active ingredient thalidomide in the medication Contergan features one form that causes birth defects during pregnancy and another form that is harmless. Separating or distinguishing between these different forms can be very difficult.
Chiral Sensing Potential Highlighted by Theoretical Studies
Three-dimensional light fields could lead to important advances in chiral sensing. Theoretical studies show that three-dimensional light fields can possess chiral properties, as noted by Wollenhaupt. The possibilities that these fields open up for investigating and controlling molecular chirality were recently highlighted by Prof. Dr Olga Smirnova of the Max Born Institute for Nonlinear Optics in Berlin. Smirnova published an article in the journal Science titled “A New Age of Molecular Chirality.”
The University of Oldenburg physicists stated that their current study lays an important foundation for such applications in molecular investigation and light-matter control.
