Key challenges in a nutshell
- Sensors need to operate in very stringent conditions (room temperature, cryogenic, high vacuum). Therefore, depending on the location of the sensor in the gravitational wave detector, a different type is required.
- The required sensitivity of the sensors varies depending on the location in the interferometer. High sensitivity sensors are necessary for detecting miniscule signals but prove more difficult to produce. However, in cryogenic conditions, smaller sensors such as microelectromechanical systems (MEMS) are more suitable and are easier to produce.
- The sensor has to possess several degrees of freedom (angles, tilting, etc.)
Short description of the technology
For the detection of gravitational waves, the Einstein Telescope will depend on highly accurate lasers and sensors. The sensors will register the disturbance caused by gravitational waves. Due to the very small wavelenghts of these waves (10-18 m), the sensors need to be extremely sensitive to detect the gravitational waves. Also the vibrations of the earth itself need to be compensated as they interfere with the accuracy of the readouts. Therefore the Einstein Telescope will push the boundaries of contemporary sensor-technology.
In this framework, two sensor concepts will be highlighted:
- Differential sensors: Optical sensor that measures vertical and horizontal movement of laser wavelengths
- Inertial sensors: Measurement of earthly vibrations with proof-mass
State of the Art: technology in existing gravitational wave detectors / TRL
- Inertial sensor developed by Joris Van Heijningen from Université Louvain-La-Neuve (TRL1)
- Photodiodes developed by NIKHEF (TRL 3)
- MEMS developed by NIKHEF (TRL 3)
Intended use in the frame of the Einstein Telescope
In the Einstein Telescope the laser beams will be guided through the 10km long arms by optical mirrors (see technology sheet of mirror technology). These optical elements need to be suspended to reduce the earthly vibrations as they are a billion times more pronounced than the gravitational waves. However, these suspension systems will not suffice in excluding all vibrations, this is where the differential sensor comes into place. The function of the inertial sensor is to measure the earthly vibrations so these can be digital excluded from the readouts. The sensor accomplishes these signals by measuring its movement against a decoupled mass. The difference in frequency is the earthly noise.
The differential sensors will measure the movement of the laser caused by gravitational waves. These photosensitive diodes will capture the laser signal over a long range and need to be sensitive enough to measures gravitational waves. The conditions in which these sensors will operate are influenced by the physical tendency of the optical instrumentation, which benefit from very cold, cryogenic temperatures and vacuum surroundings.
Improvements needed: Technological challenge for the Einstein Telescope
Sensors need to operate in very stringent conditions (room temperature, cryogenic, high vacuum). Therefore, depending on the location of the sensor in the gravitational wave detector, a different type is required.
The required sensitivity of the sensors varies depending on the location in the interferometer. High sensitivity sensors are necessary for detecting minuscule signals but prove more difficult to produce. However, in cryogenic conditions, smaller sensors such as microelectromechanical systems (MEMS) are more suitable and are easier to produce.
The sensor has to possess several degrees of freedom (angles, tilting, etc.)
Economic perspectives of participation beyond the ET applications
Developments for photodiodes and MEMS will typically come from collaborations between SMEs, knowledge institutions and mature companies. Different organizations will be responsible for different aspects of sensor technology (design and production of components, read-out of the signals; etc.).
It can be expected that these sensors will enter other markets as well (aerospace, space travel, automotive, energy (battery), telecommunication), electronics.
Related projects and labs
Globally, there are four gravitational wave observatories operational, of which two are situated on the continent of Europe.
GEO600, Ruthe Germany
The GEO600 project aims at the direct detection of gravitational waves and the development and improvement of the required technology by operation of a laser interferometer of 600 m armlength.
Virgo, Pisa Italy
Virgo is an interferometric gravitational-wave antenna. It consists of two 3-kilometre-long arms, which house the various machinery required to form a laser interferometer. The Virgo observatory was the first gravitational wave observatory (in collaboration with LIGO, USA) to detect gravitational waves in 2015. (Detection GW140915, 2015)