LZH working on lasers for ‘3rd generation’ gravitational wave detectors

28 Sep 2023

As part of "3G-GWD: Third- Generation Gravitational Wave Telescopes" joint research project across Germany.

In the joint research project “3G-GWD”, scientists at Laser Center Hannover (LZH) is working on the development of new laser sources for future, more sensitive gravitational wave detectors of the next generation.

Gravitational waves are extremely small distortions of space-time that are generated by the acceleration of objects and then propagate as waves at the speed of light. A gravitational wave hitting the earth can be measured using detectors by creating optical interference in an interferometer with a highly stable laser.

Therefore, current gravitational wave detectors use solid-state lasers at a wavelength of 1064 nm. Longer wavelengths are needed for cryogenically cooled mirrors, such as those used in next-generation detectors.

It was announced this week that the LZH scientists are to develop laser sources that emit at a wavelength of 2 µm. For this purpose, they will investigate fiber amplifiers’ dynamic behavior and power scaling with different active doping in this wavelength range.

The LZH work is part of the collaborative project known as “3G-GWD: Third-Generation Gravitational-Wave Telescopes”, in which several German scientific institutions are preparing for two international projects in the field of gravitational-wave research: the planned Einstein telescope (see below) in Europe and the Cosmic Explorer in the USA.

Partners in the project “3G-GWD: Third Generation Gravitational Wave Telescopes” are, in addition to the LZH, the Rheinisch-Westfälische Technische Hochschule Aachen (coordination), the Forschungsverbund Berlin e.V., the University of Hamburg, the Technische Universität Carolo-Wilhelmina zu Braunschweig, the Leibniz Universität Hannover, the FH Münster, the Karlsruhe Institute of Technology and the Friedrich-Alexander-Universität Erlangen-Nürnberg. The project is funded by the German Federal Ministry of Education and Research.

About the Einstein Telescope

The Einstein Telescope is a design concept for a European third-generation gravitational-wave detector, which will be 10 times more sensitive than the current advanced instruments of the second generation.

Like the first two generations of gravitational-wave detectors, the concept for the Einstein Telescope is based on the measurement of tiny changes (far less than the size of an atomic nucleus) in the lengths of two connected arms several kilometres long, caused by a passing gravitational wave. Laser beams in the arms record their periodic stretching and shrinking via brightness changes on a central photodetector.

The first generation of these interferometric detectors (GEO600, LIGO, Virgo and TAMA) successfully demonstrated the proof-of-principle and constrained the expected gravitational-wave emission from several sources.

The next generation (Advanced LIGO and Advanced Virgo), which were constructed until 2015, have made the first direct detection of gravitational waves and have observed 90 signals so far. However, these detectors will not be sensitive enough for very precise astronomical studies of the gravitational-wave sources – new detectors are required.

A multi-detector

The strategy behind the Einstein Telescope project is to build an observatory that overcomes the limitations of current detector sites by hosting more than a single gravitational-wave detector. It will consist of three nested detectors, each composed of two interferometers with arms 10 kilometres long. One interferometer will detect low-frequency gravitational wave signals (2 to 40 Hz), while the other will detect the high-frequency components.

The configuration is designed to allow the observatory to evolve by accommodating successive upgrades or replacement components that can take advantage of future developments in interferometry and also respond to a variety of science objectives. Currently, possible detector sites in the border area of Belgium, Germany, and the Netherlands as well as Sardinia are being evaluated.