Making the invisible visible

For us, it's unimaginable, but for science fiction heroes like Kirk, Spock, Kathryn Janeway, or Jean-Luc Picard, it's completely normal: in outer space, there is noise, trembling, and shaking. The inaudible and imperceptible, such as the collision of black holes, can be overheard and made visible by astrophysicists using gravitational wave detectors. Albert Einstein first mentioned gravitational waves in 1916 as a consequence of his general theory of relativity. However, they were not discovered until 2015. Research into these waves is crucial for our understanding of the universe.

Wherever the goal is to make the previously invisible visible, ZEISS SMT is never far away. Whether with a microscope in Abbe’s time or today, when ultra-precise mirrors are used to detect gravitational waves. For exactly this purpose, scientists from the Einstein Telescope project requested prototype mirrors from ZEISS SMT. They were delivered at the end of September 2024.Manufacturing gravitational wave mirrors – which are central elements of gravitational wave detectors – is anything but routine at the German Oberkochen site: “These are highly demanding one-of-a-kinds, produced by our staff in addition to regular manufacturing orders,” says Dr. Michael Mundt, Head of DUV Modules & Components.

Norman Niewrzella, Cluster Lead Special Optics, also points to the project’s challenges, which required flexibility, initiative, and perseverance. The polishing of the prototypes was especially complex. It was equally challenging to integrate them into the manufacturing process: for this, the ZEISS SMT team from R&D, engineering, manufacturing, and the specialist department developed and tested in part new processes.
 

A gravitational wave detector consists of two kilometer-long tubes in which laser beams travel back and forth. The tubes are evacuated to minimize disturbances from air molecules and equipped with vibration-damped special mirrors. The laser beams are directed onto a light sensor, creating a pattern of light and dark. When a gravitational wave passes by, the length of the tubes changes slightly, as they are stretched or compressed by the wave. As a result, the waves of the laser beams shift relative to each other, which alters the light and dark pattern on the light sensor. The detector is extremely sensitive and can measure the tiny changes in the length of the tubes and the shifts of the laser beams. By analyzing the flickering of the light and dark pattern, the detector can identify the presence of gravitational waves.