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25 Feb 2025
French photonics firm wins contract to deliver source for Laser Interferometer Space Antenna's ground station.
Exail, the France-headquartered photonics company, says it has won a contract with the French Space Agency (CNES) to develop and deliver an “ultra-stable” laser system for the planned Laser Interferometer Space Antenna (LISA) mission.
Selected by the European Space Agency (ESA) for funding back in 2017 following the successful “LISA Pathfinder” effort, and with additional support from NASA, the aim is to detect gravitational waves in space using a huge triangle of satellites positioned 2.5 million kilometers apart.
Exail’s source is due to be deployed in the ground station element of the complex mission, which is currently expected to launch in 2037 and will represent the first ever gravitational wave observatory in space.
Cosmic ripples
Exail, which said it was selected for LISA following a recent European call for proposals, highlighted its ability to develop industrial instruments offering a performance similar to what could be expected from the kind of highly tuned experimental setups more typically found in academic laboratories.
Bruno Desruelle, the firm’s head of photonics activities, added: “With this ultra-stable laser system, CNES will be able to validate the most critical sub-assemblies of the LISA mission with extreme precision.
“Exail leverages a strong expertise in the development of its flagship intelligent laser system (ILS) for the manipulation of quantum systems, and years of collaboration with academic researchers from SYRTE lab [the Sytèmes de Référence Temps Espace at the Observatoire de Paris] on ultra-stable instrument[s] for time and frequency reference applications.
“Exail will push the performance of this new laser a step further to meet CNES’ requirements in terms of frequency and power stability.”
The company says that for the mission it will leverage its expertise in micro-optic assemblies to develop a complex iodine spectroscopy module, which will allow the laser system to be ultra-stabilized thanks to the light absorption properties of iodine vapor.
Because its interferometer arms will be so long, the LISA constellation will be able to pick up gravitational waves - or “ripples” in spacetime - at much lower frequencies than is possible using terrestrial gravitational wave observatories.
In February 2016 scientists at the two Laser Interferometer Gravitational Wave Observatory (LIGO) sites in the US first detected the phenomenon predicted by Einstein, with the signals corresponding to a collision between two black holes 1.3 billion years ago.
High-precision lasers and optical components are critical hardware in the observatories, where they are used to measure tiny changes in the length of the interferometer arms caused by the cosmic ripples, and maintaining the stability and purity of the laser light has previously been described as the biggest single challenge at LIGO.
Longer interferometer arms
Thanks to its much longer arms, the LISA observatory is expected to be sensitive to gravitational waves at frequencies between 0.1 mHz and 1 Hz, which are expected from a much more diverse range of astrophysical sources.
CNES is responsible for ground qualification tests of the LISA instrument’s metrological core, a sub-assembly known as the IDS (Interferometric Detection System).
Exail’s ultra-stable laser system will equip CNES’s Optical Ground Support Equipment in Toulouse, France. “With one master laser, and four slave lasers phase-locked to it, Exail’s complex laser system will generate the ultra-stable laser radiations required for the optical test bench involved in these operations,” explained the firm.
François-Xavier Esnault, optical architect of the LISA project at CNES, added: “With their strong and long-term involvement and expertise on laser systems for high precision instruments, Exail shows once again they are keen on being part of a challenging project.
“Building on the experience gained during the prototyping phase, [the] Exail team involved in the LISA laser project do not hesitate to bring innovative ideas and technological concepts used in other applications to improve [compactness] and reliability without sacrificing performance.”
The French firm says that the LISA-related developments will help further strengthen its expertise in the field of time-frequency metrology, where it claims to be becoming a global leader.
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