Experts of the Fraunhofer IST explain fundamentals and specialized questions, among other things from the field of thin film technology. 

  • Can glass reflect heat?

    Answers from Prof. Dr. Günter Bräuer / March 30, 2022

    An example of modern glass architecture - the Harpa concert center in Reykjavik
    © Günter Bräuer

    To come straight to the point: No, assuming it is not coated. Any body with a temperature above absolute zero (-273.15°C) emits electromagnetic radiation whose wavelength λ is linked to its absolute temperature T in Kelvin (K) through Wien's displacement law (named after its discoverer, Wilhelm Wien (1864 - 1928)). Evolution endowed us with eyes with which we are able to see a tiny section of the electromagnetic spectrum, namely wavelengths of between around 400 nm and 750 nm. Longer wavelength radiation is perceived by us as heat, whilst shorter wavelength radiation tans our skin and damages it if such radiation is enjoyed to excess. For thermal radiation, we must distinguish between the near (NIR, λ = 780 ... 3,000 nm), mid (MIR, λ = 3,000 ... 50,000 nm), and far (FIR, λ = 50,000 ... 1,000,000 nm) infrared.

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  • How do you actually make glass “invisible”?

    Answers from Prof. Dr. Günter Bräuer / July 07, 2020

    Window front of the Fraunhofer IST main entrance in Braunschweig.
    © Fraunhofer IST, Jan Benz

    Glass as a material is fascinating due to a number of outstanding properties. The most important of these is its high transparency across the entire visible spectrum, which enables a color-neutral view of the outside world. But let us also take a look at the less pleasant properties of glass. A pane of glass reflects around 8.3 % of the incident light and therefore works like a weak mirror (especially against a dark background). In everyday life, these reflections may not be particularly disturbing, but with high-quality optical components they are not tolerable.

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  • What is actually a ”quantum lap”?

    Answers from Prof. Dr. Günter Bräuer / December 16, 2019

    © Fraunhofer IST

    I have taken the seventieth birthday of the Fraunhofer Gesellschaft in 2019 as an opportunity to take a closer look at the quantum leap. After all, the famous Fraunhofer lines which are direct consequences of quantum leaps. Around 1814 our namesake Joseph von Fraunhofer discovered around 570 mysterious black lines in the emission spectrum of the sun. He catalogued them meticulously, but was unable to explain their origin; this would have indeed been impossible back then, without the modern physics of the 20th century. If, for example, sunlight is broken down into its spectral colors through a high-resolution optical grating, “the corresponding colors are missing at the positions of the Fraunhofer lines”.

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  • How is vacuum actually generated? – Part 3

    Answers from Prof. Dr. Günter Bräuer / September 29, 2019

    Vacuum pumps
    © Fraunhofer IST

    Part 3 of the Answerd series “How is vacuum generated“ ends the excursion into the basics of vacuum technology with Professor Bräuer and summarizes amongst others once again the most important pump types with their application area together.

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  • How is vacuum actually generated? – Part 2

    Answers from Prof. Dr. Günter Bräuer / June 21, 2019

    © Fraunhofer IST

    ”Wind is air which is in a hurry.” In the Earth's atmosphere, airstreams flow from high-pressure areas to low-pressure areas. We experience them as winds, storms or hurricanes. The Coriolis force forms them into vortices.

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  • How is actually vacuum generated?

    Answers from Prof. Dr. Günter Bräuer / December 18, 2018

    In-situ diagnostics and model-based control of inline magnetron sputtering processes for large-area coating.
    © Fraunhofer IST, Rainer Meier, BFF Wittmar

    It is trivial: To remove gases from a given volume we have to pump. We know this from pumping of liquids. However, there are fundamental differences between pumping of liquids and pumping of gases. Liquids are incompressible, at constant temperature they don’t change their volume even if highest pressures are applied. This principle is used in hydraulic power transmission.

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  • What is actually ”vacuum”?

    Answers from Prof. Dr. Günter Bräuer / September 14, 2018

    Prof. Dr. Günter Bräuer, former Director of Fraunhofer IST.
    © Fraunhofer IST, Florian Kleinschmidt,

    At Leybold-Heraeus, at that time a market leader in vacuum plant construction, I learned the following ambiguous statement: “We’ve got a vacuum in our heads!” The ancient Greeks had already been involved with vacuums in around 500 BC. In order to make use of the vacuum technically, for instance to deposit high-quality thin films, we definitely need matter as well as electrical and magnetic fields, and, depending on the circumstances, radiation too. We use highly rarefied gases to operate low-pressure plasmas, which in turn serve as an energy source during the depositing of coatings. Nowadays, physicists define a vacuum strictly as a space containing neither matter, radiation nor force fields.

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