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laser physicists measured for the first time in millisecond accuracy of photoionization

2018-07-02

Recently, laser physicists measured for the first time in millisecond accuracy of photoionization, which measures 10-21. According to scientists at the Technical University of Munich, this is by far the highest precision obtained from microscopic world time measurements and the first absolute measurement of the photoionization time scale.

Photoionization is the process by which photons interact with the electrons in an atom. When a photon strikes the two electrons of a helium atom, the energy of the photon is absorbed by one of the electrons, or by both electrons. No matter how the energy is transferred, an electron will break away from the atom. This process, known as the photoelectric effect, was explained by Einstein in the early 20th century.


Schematic of photoionization of helium atoms

In recent years, physicists have found that from a photon to electron interaction to one of the electrons from the atom, a total of 5 ~ 15 as (1as = 10-18s). Laser physicists from the Max Planck Institute for Quantum Optics (MPQ), the University of Technology Munich (TUM) and the Ludwig-Maximilian University of Munich (LMU or the University of Munich) 850 zs (1zs = 10-21s) accurate measurement results.

To excite electrons in the helium atoms, the researchers irradiated atoms with an ultra-violet (XUV) light pulse of a second pulse width. At the same time with a pulse width of about 4 fs (1fs = 10-15s) of the infrared light pulse irradiation atom. Once the electrons are excited by the EUV light and leave the atom, the electrons accelerate or decelerate due to the electromagnetic field of the infrared light pulse. By this speed change, the physicists can measure the photoelectric effect with a precision of a second.

For the first time, researchers also determined from quantum mechanics how the energy of the incident photons is distributed between the two electrons of the helium atom in a few seconds before the emission of a particle. The helium atom has only two electrons and is the only multi-electron system that can be fully calculated using quantum mechanics. This makes it possible to make the theoretical value and experimental results fit.

Once a photon excites an electron from a helium atom and detaches it, it is possible to calculate the possible positions of the remaining electrons. The most likely location for electrons is the brightest area around the nucleus in the picture.

Laser physicists have filled the gaps in the metrology of helium atoms in quantum mechanics through the metrological experiments in a few seconds, and have therefore taken the measurement accuracy of the microscopic world to a whole new dimension.

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