In modern science, quantum effects have long ceased to be an abstraction—they are at the core of cutting-edge research. One such phenomenon, tunneling, allows electrons to overcome energy barriers that would otherwise be insurmountable under normal conditions. When a powerful laser pulse targets a hydrogen molecule, the electric field distorts its potential, creating conditions that enable the electron to escape the molecule. This process, known as tunnel ionization, becomes especially intriguing when using a laser with a rotating field: once the electron breaks free, it forms a distinctive torus-shaped structure in momentum space.
The shape and size of this electronic torus contain unique information about the molecular properties and the details of ionization. Until recently, however, scientists faced a major challenge: it was impossible to determine the precise strength of the laser field at the moment of interaction. This uncertainty prevented researchers from extracting all the valuable data the experiment contained.
A research team has tackled this problem using an innovative experimental approach. They chose the hydrogen molecule for analysis and utilized a reaction microscope capable of recording the three-dimensional momenta of all particles generated by the laser’s interaction. This method literally allows scientists to “see” the dynamics of events at the subatomic level and reconstruct the full picture of what happens after each laser pulse.
The key to success lay in combining precise measurements with an improved theoretical model. Scientists discovered that the radius and thickness of the electron torus depend on different parameters: one is linked to the field strength, the other—to the ionization energy. By developing a new model that accounts for field rotation and nonadiabatic effects, they were able to uniquely determine both unknown values using just two measurable characteristics.
Experiments showed that the energy required to ionize hydrogen in a strong field differs from standard values. Moreover, it turned out that this energy changes depending on how exactly the molecule breaks apart: whether it loses an electron and becomes an ion, or completely splits into separate particles.
According to one project participant, the new method allows not only precise measurement of parameters but also, for the first time, to obtain quantitative data on processes occurring on attosecond timescales. Researchers can now accurately determine fundamental characteristics encoded in the shape of the electron torus—something that was previously impossible.
The discovery opens up prospects for creating molecular films—frame-by-frame imaging of chemical reactions with incredible temporal resolution. This will not only make it possible to observe the rearrangement of electron shells and bond breaking, but also potentially to control these processes using light. Such an approach could lead to new technologies in materials science, photonics, and biochemistry.
The results have already attracted the attention of the scientific community, as they allow for the verification and refinement of current theories of light-matter interaction. In the future, this method could be used to study more complex molecules and reactions, significantly expanding the horizons of both fundamental and applied research.
