Goethe University physicists measure the meager effect with a new Super COLTRIMS.
Albert Einstein received the Nobel Prize for explaining the photoelectric effect: in his most intuitive form, the only atom is irradiated with light. According to Einstein, light consists of particles (photons) that transfer only quantized energy into an electron of an atom. If the energy of the photon is sufficient, it knocks out electrons from the atom. But what happens to the photon momentum in the process? Goethe University physicists can now answer this question. To do this, they have designed and constructed a new spectrometer with previously unattainable resolution.
Doctoral student Alexander Hartung twice became a father during the construction of the unit. The device, which is three meters long and 2.5 meters high, contains about as many parts as a car. He sits in the experimental room of the physics building on the Rydberg campus, surrounded by an opaque, black tent, inside of which is an extremely high-performance laser. Its photons collide with individual argon atoms in the apparatus and thus remove one electron from each of the atoms. The momentum of these electrons during their appearance is measured with extreme accuracy in the long tube of the apparatus.
The device is a further development of the COLTRIMS principle, which was invented in Frankfurt and meanwhile spread worldwide: it consists of ionizing single atoms, or splitting molecules, and then pinpointing the particle momentum. However, the transfer of photon momentum to electrons, predicted by theoretical calculations, is so tiny that it could not be measured before. That is why Hartung built the "super Coltry".
When numerous photons from a laser pulse bombard an argon atom, they ionize it. Breaking an atom partially consumes photon energy. The rest of the energy is transferred to the released electron. The question of which reaction partner (electron or atom nucleus) holds a photon momentum has been taking physicists for over 30 years. "The simplest idea is this: as long as the electron is attached to the nucleus, the momentum is transferred to a heavier particle, that is, the nucleus of the atom. As soon as it escapes, the photon momentum is transmitted to the electron," explains Hartung's head, Professor Reinhard Dorner of the Institute of Nuclear Physics. It would be similar to the wind that transfers its power to the sail of a boat. While the sail is firmly attached, the impulse of the wind propels the boat forward. However, when the ropes are torn apart, the wind momentum is transferred to the sail alone.
However, the answer that Alexander Hartung found during his experiment ̵
Hartung used a reasonable measuring device for the experiment. In order to prevent the small additional electron pulse from being accidentally caused by asymmetry in the apparatus, the laser pulse enters the gas from both sides: either to the right or to the left, and then from both directions simultaneously, which was the biggest challenge for the measuring equipment. This new method of accurate measurement promises a deeper understanding of the previously unexplored role of magnetic components of laser light in atomic physics.
Reference: "Magnetic fields change the ionization of strong fields" by A. Hartung, S. Eckart, S. Breneck, J. Rist, D. Trabert, K. Fere, M. Richter, H. San, S. Zeller, K. Heinrichs, G. Kastirke, J. Gel, A. Kalinin, M. S. Schaeffler, T. Yank, and L. Ph. H. Schmidt, M. Lein, M. Kunitski, and R. Dörner, September 30, 2019, Physics Nature .
doi: 10.1038 / s41567-019-0653-y