Physicists develop the perfect light trap

Perfect light trap

A ‘light trap’ setup is shown, consisting of a partially transparent mirror, a weak and thin absorber, two converging lenses and a fully reflective mirror. Normally, most of the incident light beam will be reflected. However, due to the precisely calculated interference effects, the incident light beam interferes with the reflected light beam between the two mirrors, so that the reflected light beam is finally completely extinguished. The thin and weak absorbent completely absorbs light energy. Credit: TU Wien

Whether in photosynthesis or in the photovoltaic system: if you want to use light efficiently, you have to absorb it as fully as possible. However, this is difficult if the absorption occurs in a thin layer of the material that normally allows a large portion of the light to pass through.

Now, research teams from TU Wien and the Hebrew University of Jerusalem have found an amazing trick that allows ray of light To be completely absorbed in even the thinnest layers: they build “light trapAbout the thin layer Using mirrors and lenses, where the beam of light is directed in a circle and then fixed on itself – exactly in such a way that the beam of light blocks itself and cannot leave the system. Thus, the light has no choice but to be absorbed by the thin layer – and there is no other way out.

This method of absorption and amplification, which has now been presented in the scientific journal Sciences, is the result of a fruitful collaboration between the two teams: the approach proposed by Professor Uri Katz of the Hebrew University of Jerusalem and developed with Professor Stefan Reuter of TU Wien; The experiment was conducted by the laboratory team in Jerusalem and the theoretical calculations came from the team in Vienna.

Thin layers are transparent to light

“Light is easily absorbed when it hits a solid object,” says Professor Stefan Rutter from the Institute of Theoretical Physics at TU Wien. “The thick black wool blanket can absorb light easily. But in many technical applications, you only have a thin layer of material available and you want to absorb the light exactly in that layer.”

There have already been attempts to improve the absorption of the material: for example, the material can be placed between two mirrors. The light is reflected back and forth between the two mirrors, passing through the material each time so there is a greater chance of absorption. However, for this purpose, the mirrors must not be perfect – one of them must be partially transparent, otherwise the light will not be able to penetrate the area between the two mirrors at all. But it also means that when light hits this partially transparent mirror, some of the light is lost.

the same light blocks

In order to prevent this, it is possible to use the wave properties of light in a sophisticated way. “In our approach, we are able to cancel all reverse reflections by means of wave interference,” says Professor Uri Katz of the Hebrew University of Jerusalem. Helmut Horner, of TU Wien, who devoted his thesis to this topic, explains: “In our method also, light first falls on a partially transparent mirror. If you simply send a laser beam into this mirror, it will be divided into two parts: the larger part is inverted, and the smaller part penetrates the mirror. “.

This part of the light beam that penetrates the mirror is now sent through the absorbing material layer and then back to the partially transparent mirror with another lens and mirror. The important thing is that the length of this path and the position of the optical elements are adjusted in such a way that the returning light beam (and its multiple reflections between mirrors) completely eliminates the beam of light reflected directly on the first mirror,” say Yevgeny Slobodkin and Gil Weinberg, graduate students who built the system in Jerusalem.

The two partial beams overlap in such a way that the light obscures itself, so to speak: although a partially transparent mirror alone would actually reflect a large portion of the light, this reflection is made impossible by the fact that the other portion of the beam travels through before returning to the partially transparent mirror.

Therefore, the mirror, which was partially transparent, is now completely transparent to the incident laser beam. This creates a one-way path for light: ray of light It can enter the system, but then can no longer escape due to the superposition of the reflected part and the directed part through the system in a circle. So the light has no choice but to be absorbed – the entire laser beam is swallowed up by a thin layer that would otherwise allow most of the beam to pass through.

strong phenomenon

“The system has to be tuned exactly to the wavelength you want to absorb,” Stefan Rotter says. “But apart from that, there are no restrictive requirements laser beam It does not have to have a specific shape, it can be more dense in some places than in others – perfect absorption is always achieved. “

not even air turbulence Fluctuations in temperature can also damage the mechanism, as shown in experiments conducted at the Hebrew University of Jerusalem. This proves to be a powerful effect that promises a wide range of applications – for example, the presented mechanism could be well suited for capturing light signals distorted during transmission through the Earth’s atmosphere. The new approach could also be of great practical use for optimal feeding of light waves from weak light sources (such as distant stars) into the detector.


What color is the mirror? Explain mirrors and how they work.


more information:
Yevgeny Slobodkin et al., an ideal coherent, exponentially degraded absorber for arbitrary wavefronts, Sciences (2022). DOI: 10.1126 / science.abq8103. www.science.org/doi/10.1126/science.abq8103

Presented by Vienna University of Technology

the quote: Physicists Develop Perfect Light Trap (2022, Aug 25) Retrieved August 26, 2022 from https://phys.org/news/2022-08-physicists.html

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