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Zeptosecond Measurement Achieved

Category: Science & Technology
Posted: 12:45PM
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Albert Einstein is remembered for many contributions he made to physics, but the one he earned the Nobel Prize for was the Photoelectric Effect. This phenomenon converts optical energy to electrical energy and back, and is at the core of many modern technologies, including LEDs and solar panels. More than one hundred years after Einstein's paper was published, researchers at the Vienna University of Technology and Technical University of Munich have made unprecedented measurements of photoionization in progress, a process the photoelectric effect explains.

For this study, the researchers worked with a helium atom, as it is the simplest and best understood multi-electron system. By firing a short, high energy laser pulse at it, one of the atom's two electrons can absorb enough energy to leave the atom, and thanks to quantum mechanics it is possible for the second electron to also absorb some energy, but this does not always happen. This means there are actually two different photoionization processes that can occur. In either case though, one electron is ejected from the atom and the researchers caught this with another infrared laser pulse, and it turns out the process that excites this second electron is faster than the process that does not.

Both photoionization processes occur over attoseconds, which are 10-18 or 0.000000000000000001 seconds, so to make this measurement the researchers had to be even more precise, reaching into zeptoseconds (10-21 or 0.000000000000000000001 seconds). The way the researchers measured with such precision was by catching how the infrared laser pulse affected the speed of the emitted electron. Depending on the electromagnetic field of that pulse, the electron would either speed up or slow down, and that change allowed the researchers to measure events at a rate of 850 zs. The difference between the two processes was about 5 as, which agrees with the theoretical simulations run by the Vienna Scientific Cluster supercomputer.

Beyond setting new records, this discovery will allow for the derivation of a complete wave mechanic description of the interconnected system of an emitted electron and its mother helium ion. It also shows the effects believed to be instantaneous decades ago can actually be measured and even controlled.

Source: Vienna University of Technology and the Technical University of Munich



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