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Light, matter - and everything in between

on materials with a large refractive index, from which optical components such as camera lenses, microscopes, imaging systems, mirrors and filters can be developed

Metamaterials are engineered, semi-synthetic materials with unique properties that do not exist in nature, which are created due to their artificial structure. Dr. Tomer Levy from the Faculty of Engineering at Bar-Ilan University and his team engineer materials, thus turning them into metamaterials, and study their interaction with light. This is to understand the physics involved in this interaction and to develop flat optical components, such as camera lenses, microscopes, imaging systems, mirrors, beam splitters (components that split light rays), polarizers, holograms and filters.


It is possible to obtain wonderful physical properties from the interaction of light and engineered material, ones that do not occur in nature,



"It is possible to obtain wonderful physical properties from the interaction of light and engineered material, ones that do not occur in nature, and develop advanced optical components based on them - almost every optical component that exists in the laboratory and in industry," says Dr. Levy. "It is possible, for example, to create square structures on the surface of silicon using photolithography methods and shine a laser on it - and thus succeed in introducing 100% of the light into it instead of 70% in its normal state. That is, to create a situation where the reflection of light is zero."

Dr. Levy and his team also investigate surface properties of exotic materials. For example, two-dimensional materials (consisting of a layer one atom thick) such as graphene and topological insulators. This is because these are unique properties that contribute to the high mobility of electrons on the surface, thus making it possible to produce tiny and advanced opto-electronic components such as detectors and modulators.

The refractive index of bismuth telluride (Bi2Te3) as measured in the laboratory in the infrared field.

In their latest study, which won a grant from the National Science Foundation, the researchers focused on a group of substances called chalcogenides - compounds that contain at least one element of sulfur, selenium or tellurium. Some such compounds include lead telluride, bismuth telluride, and bismuth selenide. In a previous study, the researchers discovered that these materials are characterized by a refractive index that varies in intensity depending on the temperature. This coefficient is the most significant index in the field of optics; It is the one that determines how much the light is refracted (reflected), absorbed or scattered, when it hits a certain medium. The larger this index is, the more it is possible to perfect optical applications (such as the focal length of a lens and the dispersion of light in different directions).

The researchers engineered surfaces from chalcogenides, heated or cooled them using an electric current and thus affected their properties. "Dynamic control of a metasurface dramatically changes its properties, for example, it can turn it from completely transparent to 100% reflective, a perfect look," explains Dr. Levy.

Among other things, the researchers engineered telluride lead surfaces and heated them using an electric current. This is how they actually created a dynamic optical filter (spectral filter) - a device that passes light rays according to their properties (such as color and polarization), and blocks the rest of the rays that do not have these properties, which can be opened and closed depending on the electrical voltage. Such a filter, small and electrically controlled, can be integrated, for example, in sensors and spectrometers (optical measuring instruments for observing the radiation range of light sources) and contribute to their miniaturization, so that they are more advanced, easier to operate and cheaper. Today, many spectrometers have optical filters consisting of many moving mirrors with light echoing between them. Dr. Levy says that "instead of a system that is tens of centimeters long and weighs about a kilogram, we developed a surface that weighs ten grams and the length of the active part is less than a micron. We tested it with calculations and simulations and saw that it works as expected."

In addition, the researchers measured the refractive index of the material bismuth telluride and found that it is the largest ever measured. Therefore, surfaces were engineered from it whose resolution is ten times smaller than the wavelength of the light that hits them. This way you can spatially control the light, compress it into small optical components and get a much higher resolution. "We discovered that it is possible to engineer dynamic, tiny and highly efficient surfaces also from bismuth telluride to be used for advanced optical components. Because, the greater the refractive index, the stronger the interaction of the light with the material", concludes Dr. Levy.

Life itself:

Dr. Tomer Levy, in a relationship + two daughters (7, 9), lives in Tel Aviv. Loves tennis, music, cinema and traveling.

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