GT4ET
Glass Technologies for the Einstein Telescope (2022-2025)
From January 2022 to December 2025, researchers at the Max Planck Institute for Gravitational Physics in Hannover collaborated with colleagues from the Fraunhofer Institute for Applied Optics and Precision Engineering (Fraunhofer IOF) on the “Glass Technologies for the Einstein Telescope” (GT4ET) project. Together, they developed novel, miniaturized opto-mechanics for the Einstein Telescope, the planned European third-generation gravitational-wave detector, and investigated new methods for laser power stabilization.
New technologies for the Einstein Telescope
Currently, scientists are preparing new, more sensitive gravitational-wave observatories on Earth that will begin operating in the 2030s. These third-generation detectors will observe a similar frequency range as current instruments but will be up to 10 times more sensitive. The European project is called the Einstein Telescope.
AEI Hannover has long been a leading institution in gravitational-wave research. It is a co-initiator of the Einstein Telescope and is involved in several areas of its preparation.
To enable the significantly increased sensitivity, larger detector systems and further technical improvements are required. The "Glass Technologies for the Einstein Telescope" (GT4ET) project, a collaboration between the Max Planck Institute for Gravitational Physics (Albert Einstein Institute, AEI) in Hannover and the Fraunhofer Institute for Applied Optics and Precision Engineering (Fraunhofer IOF), developed new technologies for seismic isolation and laser stabilization for the Einstein Telescope.
Highlights of GT4ET research
Developing sensors for improved seismic isolation
The main optical components of laser interferometric detectors, such as mirrors and beam splitters, must be largely decoupled from ground movement (seismic noise) by complex mechanical filter structures. To achieve this, the optical elements will be suspended from multi-stage pendulums. These pendulums dampen seismic noise and are also used in current gravitational-wave detectors.
Active damping requires precisely determining the positions of the individual masses within the suspension pendulum chain relative to a reference point. For this purpose inertial sensors are used. Their performance depends heavily on their mass. The state-of-the-art sensors used in current gravitational-wave detectors have masses of several kilograms. Only with a carefully designed sensor can its size and weight be reduced without compromising performance.
GT4ET researchers have developed a compact inertial sensor with a mass in the gram range and tested it in a gravitational-wave detector prototype. They have demonstrated that its performance is on par with that of commercially available sensors currently used in gravitational wave detectors, which have masses in the kilogram range.
Thanks to its small size, self-calibration, inherent vacuum compatibility, and plug-and-play functionality, the sensor is ideal for integration into a wide range of applications. These applications include complex seismic isolation systems for future gravitational wave detectors, such as the Einstein Telescope or the Cosmic Explorer.
Laser stabilization with micro-oscillators
The properties of the lasers used in gravitational-wave detectors are actively stabilized to minimize noise in frequency, power, and beam geometry. The AEI has many years of experience developing, stabilizing, manufacturing, and installing lasers for gravitationa-wave interferometry on Earth.
A new method of stabilizing laser power for gravitational-wave detectors is currently being investigated and has already yielded promising initial results: power stabilization using a micro-oscillator. As part of GT4ET, the AEI and the IOF have further examined this technology and implemented a concrete concept for it.
