The quickest and smallest details of the electron dynamics in atoms were imaged by a global team headed by scientists from the Cluster of Excellence PhoenixD at Leibniz University Hannover (Germany). The imaging was done using light with wavelengths, which were thus far considered way too long for this particular task.
Image Credit: Shutterstock.com/ vchal
The discovery will allow novel, much easier access to the smallest temporal and spatial scales in the atomic world.
Dr. Ihar Babushkin, Theoretical Physicist, Leibniz University Hannover
Dr. Ihar is also a member of the Cluster of Excellence PhoenixD at LUH.
How can an individual calculate the flight path of a butterfly while the lowest scale on the ruler is as huge as the Empire State Building? This question might sound ridiculous because, usually, nobody would want to measure a tiny animal with a scale that is many times larger.
To perform this task, a tape measure is needed, for which the unit of measurement is less than that of a butterfly. Those size differences could also be identified in the smallest particles: For instance, the atom size is calculated with the unit of Ångström.
One Ångström is equal to a ten-millionth part of a millimeter (10-10 meters). Now, if atoms are calculated using light, the wavelength of the light acts as the measurement unit — the “division of the ruler.”
Ultimately, wavelengths in the Ångström range must be the most appropriate for this task. These will be X-Rays, and an observer will not be expected to observe much or anything at all while looking for the atom in visible light that comes with a 3000 times longer wavelength.
Such rules of ratio apply to the observation of both space and time: For example, the tunneling of an electron away from the atom, while the latter is located in a very high-intensity electric field, is one of the fastest processes in atomic physics. Ionization occurs at attosecond time scales (which is 10-18 seconds), while the time taken for a single oscillation of visible light is approximately one femtosecond (which is 10-15 seconds).
To study processes like this, researchers use up to now much shorter light wavelengths or the electrons escaping the atoms. Both types of measurements have significant disadvantages—they are difficult to produce and handle. But we found a solution.
Dr. Ihar Babushkin, Theoretical Physicist, Leibniz University Hannover
His research was financially supported by the DFG (German Research Foundation) Priority Program 1840 (QUTIF), initiated and coordinated by LUH.
A new method to access the tiniest atomic scales was discovered by a group of 21 researchers who were led by members of the Cluster of Excellence PhoenixD. Using this research, they proved that electron dynamics’ clear signatures are preserved in visible light — on the time and space scales.
Furthermore, far longer wavelengths — down to the millimeter (terahertz) range — could be also be used. This implies that it is possible to level up the dynamics from the atomic level to the macroscopic size. This discovery was published in the journal Nature Physics.
In strong fields, during the course of ionization, the electron leaves the atom and is eventually accelerated. Electron radiates light, like any accelerated charged particle. As the duration of the ionization process is very short, the radiation spectrum is very broad and comprises components in visible, ultraviolet and even terahertz ranges.
Looking at the polarization of the emitted light is the key here. The polarization is very sensitive to even the tiniest of details of the electron dynamics. “Measuring light polarization allows reconstructing many aspects of electron dynamics with excellent precision,” stated Babushkin.
New opportunities are opened up by the new type of imaging: It ensures experimental setups are cheaper than before and hence affordable to a wider variety of scientists across the globe.
Besides, this allows us to observe the electron dynamics in situations when neither light at short wavelengths nor electrons are available for detection, for instance, in the bulk of solids.
Ayhan Demircan, Theoretical Physicist and Member, Cluster of Excellence PhoenixD, Leibniz University Hannover
Ultimately, optical polarization calculations can be very accurate, therefore, enabling scientists to measure the electron dynamics more precisely than ever before.
“In the future, these findings will contribute to our understanding of the light-matter interaction at the edge of possible resolution both in time and space,” Babushkin concludes.
Journal Reference:
Babushkin, I., et al. (2022). All-optical attoclock for imaging tunnelling wavepackets. Nature Physics. doi.org/10.1038/s41567-022-01505-2.