Key technology for the Einstein Telescope reaches next milestone

High-precision laser from Hannover is used in new test environment

To the point:

• Key technology for ET: The Einstein Telescope (ET) is Europe's future gravitational-wave observatory. The ETpathfinder research and development facility in Maastricht is testing key technologies for ET. One such technology is a novel laser source from Hannover.
• Laser light in a vacuum system: The laser source was developed jointly by the Max Planck Institute for Gravitational Physics and Leibniz University Hannover. Its light is now being used for the first time in the ETpathfinder's vacuum system.
• Groundbreaking research: These results will be instrumental in the development of future laser sources for gravitational-wave detectors, such as ET and the US Cosmic Explorer project.

Important step

For the past few years, researchers at the Max Planck Institute for Gravitational Physics (Albert Einstein Institute, AEI) and Leibniz University Hannover have been working together to develop a high-precision laser source for the next generation of gravitational-wave detectors. In 2024, the team transferred the technology from their Hannover laboratory to the ETpathfinder test facility in Maastricht. They set up the laser source in the new clean room environment and conducted numerous tests.

The team has now reached an important milestone: they have relocated the laser source so that its light can circulate in the vacuum system of the large-scale ETpathfinder experiment for the first time, where it will be coupled with optical components. The researchers will conduct further tests of the laser system. The goal is to fully integrate it into the large-scale experiment and related research and development work. This will the enable high-precision measurements of the planned European Einstein Telescope.

On the way to the goal

“This brings us one step closer to the final integration of our Hannover laser source into ETpathfinder,” says Nicole Knust, a PhD student at the AEI in the Laser and Squeezed Light working group. “We fed the light from our laser source into an optical resonator, a kind of light storage and filter device, in the vacuum system. In the next step, we will use this resonator to further improve the laser light and to tune it more precisely.”

Third-generation gravitational wave detectors, such as the Einstein Telescope in Europe and the Cosmic Explorer in the US, differ from current instruments in several key ways and require new technologies. These include new laser sources with different wavelengths: The laser source developed at the Max Planck Institute for Gravitational Physics and Leibniz University Hannover generates high-precision infrared laser light at a wavelength of 1550 nanometers and a power of up to 10 watts.

“At ETpathfinder, we can build on and further expand our decades of experience in developing laser sources for gravitational-wave detectors on Earth,” explains Benno Willke, who leads the Laser and Squeezed Light working group. “This is excellent preparation for our contributions to the Einstein Telescope and Cosmic Explorer, the third-generation detectors on Earth.”

ETpathfinder

ETpathfinder is a research and development facility in Maastricht operated by a collaboration of more than twenty research institutions from seven European countries. It enables researchers to collaborate in one location to develop and test innovative technologies required for ET and to investigate their compatibility.

Research funding

The QuantumFrontiers Cluster of Excellence, through its Topical Group “Laser Development and Stabilization for Next-Generation Gravitational-wave Detectors” and the German Federal Ministry of Research, Technology, and Space have funded the development of the laser system for ETpathfinder.

Background

Moving a high-tech experiment from one location to another – even if it is only a few meters – is a complex undertaking, as the system consists of many sensitive, high-precision optical components, the associated control technology, and cabling.

Therefore, every step, every component, and the entire experiment are precisely documented. This allows changes in functionality to be classified later, the technology to be developed further, and errors to be found and corrected.