Extreme-Ultraviolet Meta-Optics for Attosecond Microscopy

Semiconductor structures of the future, such as innovative solar cells, novel nano-catalysts, or communication devices that exploit quantum properties, have in common that they consist of tiny units and exploit processes that occur on extremely short time scales. Even today, transistors - the switches in our computers and cell phones - are only a few tens of nanometers in size. 1 nanometer corresponds to 0.000 000 001 meters = 10-9 meters - for comparison: 10 000 such transistors laid on top of each other would only be as thick as a single sheet of paper. Moreover, processes that take only a few 100 attoseconds can decide whether a nano-device works or not - for illustration: the ratio between 1 attosecond and 1 second corresponds to the ratio between 1 second and the age of the universe. An example of such an ultrafast process is the absorption of light, which determines whether a solar cell is efficient or not. The observation of such processes in miniature devices is complex due to the extreme resolution needed, but central for the development of future technologies. The first goal of the EUVORAM project is to design novel optics and then build a microscope that combines very high spatial and very high temporal resolution. To achieve this, the microscope will use extreme ultraviolet light. This radiation is invisible to us and oscillates much faster than visible light, which distinguishes it for ultrafast observations. However, for light in this spectrum, no good optics exist yet. Therefore, it is difficult to achieve a good spatial resolution. EUROVAM will use so-called meta-optics for this purpose. Lenses focus light by creating a phase shift. This happens because light oscillates faster in the glass of a lens than in air. In regions where a lens is thick, the phase shift is larger; in thin regions, it is smaller. Today, modern nanoscience allows us to produce the same effect without polishing glass. The new approach is to use billions of tiny nanopillars. Each nanopillar has a precisely designed cross-section that is previously computed to produce the desired phase shift. Lenses made with this technique can be extremely thin, making them especially suitable for extreme-ultraviolet light. Because these lenses are composed of many tiny optical building blocks, they are called metalenses. The second goal is then to use the new microscope to understand the most elementary processes in, for example, today`s state-of-the-art switches, solar cells, and other optoelectronics. With this knowledge, we can make the next generation of technology even faster, even smaller, and even more energy efficient.