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The ETpathfinder R&D lab

The Einstein Telescope has to be far more accurate than existing gravitational-wave observatories. This will require new and better technologies, some of which still have to be developed. That will be done in a special R&D laboratory: ETpathfinder. Here, scientists and businesses will work together on vacuum systems, cooling systems, mirrors and mirror coatings, vibration dampers and measurement and control software. Although concerned primarily with technology for the detection of gravitational waves, this lab is also bound to generate new know-how with wider applications.

ETpathfinder: a unique R&D lab

The idea of an R&D laboratory for gravitational-wave observatories is not new. The existing LIGO and Virgo facilities could never have been so precise without R&D back-up from labs in Glasgow, Munich and California. But ETpathfinder will go one step further by making it possible to perform tests at extremely low temperatures. It is to be the first facility of its kind able to cool silicon mirrors. That is an important step in suppressing noise, for even more precise measurements. Because this is unique, it will attract scientists and businesses from all over the world.

Co-operation between science and industry

Fifteen scientific institutions in the Netherlands, Belgium and Germany are currently involved in ETpathfinder, and committed to collaborating with industry partners. It is important that these firms come on board as soon as possible, so that they can participate actively in the lab’s R&D work and guarantee the viability of its new technologies. When companies and scientists work together, new expertise and know-how are generated. Not only are they important for the construction of the Einstein Telescope, but the businesses involved can use the technologies thus developed to create and market new products.


In August 2019, a site for ETpathfinder was acquired at Duboisdomein 30 in Maastricht. Construction is due to begin in the spring of 2020 and the cleanroom is scheduled for completion in 2021. The laboratory is expected to be fully operational in 2022. The facility will remain in use for at least ten years.

What it looks like and how it works

ETpathfinder will be a testing ground for laser interferometry, the technique used to detect and measure gravitational waves. You can see how that works in this video:

A laser beam is split into two and reflected by mirrors at the ends of the “arms”. The two beams then come together again and are collected on a detector. When they do so, they either cancel out one another on the detector or are amplified. This depends on the difference in length between the arms. When a gravitational wave passes it distorts space-time by a minuscule amount so that one of the arms is very briefly a tiny bit shorter than the other. This produces a flicker in the signal, which the detector picks up: the gravitational wave’s fingerprint.

ETpathfinder will have a cleanroom, a large dust-free hall with a stable temperature. Various configurations of the laser interferometer can be set up here over the next twenty to thirty years. The core installation will have two arms, each 20 metres long. That is not big enough to actually observe gravitational waves, but it is sufficient to develop and test all kinds of relevant techniques.


impressie van ETpathfinder
Illustration: Marco Kraan, Nikhef
The set-up consists of a number of towers containing vibration-free tables. The laser source and detector are located in the central towers. The laser light is split into two beams, which are directed into the two “arms”. In four towers along these arms are mirrors with a special coating, which reflect the laser light back and forth. The mirrors can be cooled down to -153 °C, and in the future perhaps even to -263 °C!

More information

Visit the ETpathfinder website for more detailed information about the facility and the project.