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Stone Stories: Heavy-weight granite table for tiny surface structures

(September 2011) Opposites could hardly be greater: a 19 t laser, which enables precision of a billionth m (nanometre). Granite is used because of its special properties: it transmits practically no vibration, does not react to changes in temperature and has practically no inside strain. And: since the crystal structures are extremely dense, it allows for very even, smooth surfaces as needed for precision equipment with integrated air buffers.

The new laser-research-centre of the Swiss Federal Laboratories for Materials Science and Technology (Empa) took up work in Thun recently. Here innovative surface structures are tested and developed as needed e.g. to reduce aerodynamic drag to an absolute minimum or to prevent battening down and thriving of fungi. The research can be useful e.g. in airplane and shipbuilding, lighting or even for new types of windowpanes to name but a few areas of application.

The base of the apparatus is comprised of a granite block 4.60 m x 2.10 m and 50 cm thick with an integrated precision cut groove to guide the 1.7 t (2 m x 1.5 m x 20 cm) air-cushioned table, onto which the samples are mounted. The super-smooth granite surface prevents air escaping from the cushion during the course of the experiment.

Bridged pillars upon which a second table is mounted, provide the anchoring for the optical lens and the laser directing the bundled ray which cuts the surface of the sample.

The set-up is unique not only in its ability to produce high-precision surface-structures. It is also the only apparatus of its kind world wide in which objects measuring up to 3 m² can be fabricated.

Empa (Swiss Federal Laboratories for Materials Science and Technology)