University of São Paulo: Magnetic lenses are on the border between geometric and wave optics

An article published by researchers from the Soft Matter Laboratory of the School of Arts, Sciences and Humanities (EACH) at USP was considered one of the most interesting works of the year 2021 by the scientific publication Optics and Photonics .

The work, entitled Horocycles of Light in a Ferrocell , sought to investigate the optical processes involved in the formation of light patterns created by a ferrocell lens under the effect of a magnetic field.

Ferrocell is a type of magnetic lens made from ferrofluid, a liquid that contains iron nanoparticles wrapped in a detergent, also called a “ smart fluid ” . As it has magnetic properties, it is possible to change the path of light that passes through it by generating magnetic fields through magnets or coils. This technology is used in didactic experiments in magneto-optics, cell phone and computer screen displays and in optimizing the operation of solar panels, for example.

This new study sought to investigate the optical processes involved in the formation of light patterns created by a ferrocell lens under the effect of a magnetic field, whose scientific basis had not yet been detailed through analysis and structured experiments.

For this, the researchers observed the behavior of a beam of light that passed through a ferrocell lens combined with a magnet and noticed that it forms a circular luminous pattern called a horocycle (a geometry term for this type of curve made up of several lines that converge at the same point), which changes its appearance according to the position of the observer, as can be seen in the video below:

Furthermore, the main discovery was that this system reflects and diffracts light at the same time, which means that it operates within the rules of geometric optics and wave optics simultaneously, something peculiar within classical physics.

“This system is like a ‘platypus’ in optics: it has characteristics of two different concepts from classical physics, waves and rays. When we establish that we are working with something on this frontier, we enable the development of devices that use ferrofluids to be carried out with an understanding of the scientific bases of the phenomena at stake, which allows us to know the ideal conditions for the system to work”, he explains. physicist Alberto Tufaile, first author of the article.

According to him, this work opens space for other groups to better understand how this system works and to perform numerical simulations to see if they find the same results.

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