This effect, the so-called collective Lamb shift, was recently observed by a research team headed by Dr. Ralf Röhlsberger from the Helmholtz research centre DESY. The scientists from DESY, ESRF (France) and University of Leuven (Belgium) provided evidence of an effect that theorists predicted already more than 35 years ago, but could not be experimentally proved so far. The results of this experiment carried out at ESRF in Grenoble are published in the current issue of Science.
The Lamb shift is a small difference of the oscillation frequency of electrons in the atom. It becomes visible when light excites atoms to radiate. The frequency shift occurs when the excited atom emits and re-absorbs its light several times before returning to its ground state. The discovery of the Lamb shift in hydrogen in 1947 laid the foundation for the development of quantum electrodynamics (QED) as a unified theory of interaction of light and matter. For this discovery, the physicist Willis Lamb received the Nobel Prize in 1955.
When an ensemble of identical atoms is excited to radiate, it is possible that the emitted light of an atom is not only absorbed and re-emitted by the single atom but also by other atoms of the ensemble. Therefore, the light emitted by these atoms has a lower energy and exhibits a distinct red shift compared to the light that a single isolated atom would emit.
For their experiments, Röhlsberger and his team of researchers developed a new measurement method. They placed an ensemble of 57Fe atoms between two platinum mirrors separated only by a few nanometres and irradiated this array with X-ray radiation. And in fact, the predicted collective frequency shift could be measured in this way, even though it was believed for a long time that the atoms must not be separated by more than a wavelength. The researchers’ group took advantage of the fact that that the radiation of 57Fe atoms is enormously intensified, making the collective Lamb shift clearly visible. With the help of Mössbauer spectroscopy, the shift could be determined very precisely. The measured values are in excellent agreement with theoretical predictions.
This experimental method also offers new possibilities to study collective effects in the interaction of light and matter. Thus, the researchers observed that the light from the ensemble of atoms was emitted almost 100 times faster than from a single isolated atom. This phenomenon is called superradiance. Superradiance enables a very efficient energy transfer between light and matter and it may play an important role for designing more efficient solar cells and in fast optical information processing.
Dr. Thomas Zoufal | idw
Astrophysicists measure precise rotation pattern of sun-like stars for the first time
21.09.2018 | NYU Abu Dhabi
Halfway mark for NOEMA, the super-telescope under construction
20.09.2018 | Max-Planck-Institut für Radioastronomie
The building blocks of matter in our universe were formed in the first 10 microseconds of its existence, according to the currently accepted scientific picture. After the Big Bang about 13.7 billion years ago, matter consisted mainly of quarks and gluons, two types of elementary particles whose interactions are governed by quantum chromodynamics (QCD), the theory of strong interaction. In the early universe, these particles moved (nearly) freely in a quark-gluon plasma.
This is a joint press release of University Muenster and Heidelberg as well as the GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt.
Then, in a phase transition, they combined and formed hadrons, among them the building blocks of atomic nuclei, protons and neutrons. In the current issue of...
Thin-film solar cells made of crystalline silicon are inexpensive and achieve efficiencies of a good 14 percent. However, they could do even better if their shiny surfaces reflected less light. A team led by Prof. Christiane Becker from the Helmholtz-Zentrum Berlin (HZB) has now patented a sophisticated new solution to this problem.
"It is not enough simply to bring more light into the cell," says Christiane Becker. Such surface structures can even ultimately reduce the efficiency by...
A study in the journal Bulletin of Marine Science describes a new, blood-red species of octocoral found in Panama. The species in the genus Thesea was discovered in the threatened low-light reef environment on Hannibal Bank, 60 kilometers off mainland Pacific Panama, by researchers at the Smithsonian Tropical Research Institute in Panama (STRI) and the Centro de Investigación en Ciencias del Mar y Limnología (CIMAR) at the University of Costa Rica.
Scientists established the new species, Thesea dalioi, by comparing its physical traits, such as branch thickness and the bright red colony color, with the...
Scientists have succeeded in observing the first long-distance transfer of information in a magnetic group of materials known as antiferromagnets.
An international team of researchers has mapped Nemo's genome, providing the research community with an invaluable resource to decode the response of fish to...
21.09.2018 | Event News
03.09.2018 | Event News
27.08.2018 | Event News
21.09.2018 | Physics and Astronomy
21.09.2018 | Life Sciences
21.09.2018 | Event News