University of Oldenburg physicists have generated three-dimensional light fields by superimposing two ultrashort laser pulses, creating electronic quantum states that were previously inaccessible in experiments. The team demonstrated the technique using potassium atoms to excite and release electrons while capturing successive stages of their quantum evolution.
Laser Beams Converge in a Vacuum Chamber to Sculpt Light Fields
To create the three-dimensional light fields, researchers used an interferometer to split laser light into two beams of different colors. They then superimposed these femtosecond laser pulses—which last just a few millionths of a billionth of a second—so they intersected at a single point inside a vacuum chamber, according to the University of Oldenburg. This setup allowed the electric fields to oscillate in all three spatial directions simultaneously.
The method expands the experimental optics toolkit with a new class of light fields. Darius Köhnke, a PhD student in the Ultrafast Coherent Dynamics research group, noted that these fields open new possibilities for investigating specific light-matter interactions. Although theorists had spent decades predicting that fully three-dimensional light fields would enable novel forms of quantum control, the ability to produce such fields in a lab setting remained elusive until now.
Potassium Atoms Reveal Electron Dynamics at Ultra-High Speeds
The research team demonstrated the technique by applying their 3D light fields to potassium atoms. They selectively excited electrons within the atoms into higher-energy states and then ionized them, releasing the electrons from the atoms entirely. By adjusting the light field’s parameters, the scientists were able to determine which pathways the electrons would take upon exit and which excited states were populated.
The experiment functioned like an ultra-high-speed camera for quantum processes. Because the laser pulses are extremely short, the team observed changes in electron states at closely spaced time intervals. These measurements captured successive snapshots of the evolving quantum system, forming a visual record of quantum-state evolution.
Chiral Molecules Present New Targets for Advanced Light Fields
The new method holds significant promise for investigating chiral molecules, which are essential in biology and medicine. These molecules exist in two mirror-image forms that cannot be superimposed, 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 exhibit different properties.
For example, the active ingredient thalidomide in the medication Contergan features one form that causes birth defects during pregnancy and another that is harmless. Separating or distinguishing between these different forms remains very difficult. Three-dimensional light fields could lead to important advances in chiral sensing, laying an important foundation for such applications.
Details of the femtosecond laser and potassium experiments
How short are the laser pulses used to generate the 3D light fields?
The femtosecond laser pulses used by the University of Oldenburg team last just a few millionths of a billionth of a second.
What element did the physicists use to demonstrate the technique?
The research team demonstrated the method using potassium atoms, which served as a workhorse for the atomic physics experiments.
Which scientific journal published the research?
The findings were published in the science journal Physical Review Research.
Why are chiral molecules difficult to analyze?
Chiral molecules exist in two mirror-image forms that cannot be superimposed and often possess different properties, making them hard to separate and distinguish.
Related reading