Key challenges in a nutshell

  • Key technology of the 3rd generation Gravitational Wave Detector (GWD)
  • Narrow linewidth, high stability, high power at a wavelength of 2090 nm
  • Crystal-based oscillator seeder with a two- stage fiber amplifier
  • Additional thulium-doped fiber lasers for pumping

Short description of the technology

Current activities in the extended EMR area aim at the development of key technologies for a third-generation gravitational wave detector, also known as Einstein Telescope. Gravitational wave detectors provide an alternative view into interstellar processes, such as the collision of stars and supernovae, which can be detected by specific signatures in the form of gravitational waves, and thus represents an important addition to other established observation methods, such as optical or radio telescopes in the exploration of the universe.

The Einstein Telescope itself will be a highly precise interferometer to measure the gravitational waves. By measuring the change of the interference pattern of two laser beams, the occurrence of a gravitational wave can be observed and validated. For this, the laser will be one of the key technologies for the functionality and has highly demanding requirements: Since the gravitational waves are very hard to measure, a laser beam source with an extremely narrow line width, a high stability and high power at a wavelength of ca 2090 nm is needed.

In the current design a crystal-based oscillator seeder will be used for the generation of the narrow-linewidth radiation, which will be amplified within a two-stage holmium-doped fiber amplifier. For the pumping of the crystal-based seeder and the holmium-doped fiber amplifiers, additional thulium-doped fiber lasers will be developed.

State of the Art: technology in existing gravitational wave detectors / TRL

Lasers are being used in GWD at wavelengths of 1 µm and 1.5 µm. Fiber lasers at 2 µm are commercially available. The achieved linewidths and stabilities are not sufficient for GWD (Gravitational Wave Detectors).

Intended use in the frame of the Einstein Telescope

The developed laser system will be the beam source of the interferometer. For the generation of the laser radiation a crystal-based oscillator seeder will be used, while for amplification a two-stage fiber amplifier will be developed. The full system shall meet the following parameters:

  • Beam source with an output power of > 5 W
  • Wavelength ~ 2090 nm
  • Narrow linewidth
  • Linearly Polarized
  • Diffraction limited beam quality / TEM00
  • High power stability
  • High Frequency Stability

For the pumping of this laser beam source, another beam source with the following parameters will be developed:

  • Beam source with an output power of > 25 W
  • Wavelength ~ 1950 nm
  • Linearly Polarized
  • Diffraction limited beam quality / TEM00
  • High power stability
  • High Frequency Stability

Improvements needed: Technological challenge for the Einstein Telescope

  • Seed lasers with lower linewidth, higher stability and more power for easier amplification
  • Optical components with a higher power capability and lower noise
  • New fiber material with lower degradation effects (e.g. photo darkening) and higher practicability (e.g. easier to splice, higher efficiency)
  • High quality crystal material and high precision crystal-surface manufacturing
  • Improvement of general stability of lasers:
  • Driving electronics
  • Temperature stabilization
  • Thermal housing
  • Mode cleaning from fiber laser output toTEM00 at 2 µm
  • Measurement devices (e.g. beam detection cameras, detector cards)

Economic perspectives of participation beyond the ET applications

Lasers of this kind can find additional applications e.g. in the fields of measuring technology, quantum technology or communication technology in the future.

We are open to any other companies’ proposals.

Related projects and labs

Within the E-TEST project working on a prototype of the Einstein telescope, the Fraunhofer ILT is responsible for the laser development. Other partners in the field of optical engineering are the University of Hasselt (sensors), CSL Liège and KU Leuven dealing with the development of large silicon mirrors (manufacturing, test and coating). The University of Maastricht is in charge of the system engineering and the development support.

Ongoing and future procurements

Although a technology set consisting of most fiber components, pump diodes, passive and actively doped fibers, driving electronics and equipment for the temperature stabilization is already available for the build-up, there is the ambition to integrate new components for further improvement of the full laser system.

Technology contact

Patrick Baer
Fraunhofer ILT DE –

Business Development contacts

Peter Gier

Dirk Kalinowski

Michel Stassart
Skywin BE –

Maxime Corvilain
POM Limburg BE –

René Kessen