Spaceborne Earth observation with laser-based instruments is essential to gain deeper insight in large-scale atmospheric dynamics, improve the climate modelling and enhance the monitoring of the planet’s surface regarding the impact of climate change. The currently used laser systems rely on the well-established Nd:YAG laser material. Alexandrite is investigated as alternative due to its broad spectral bandwidth and thus tunable output wavelength and the high optical efficiency. Besides, it features excellent material properties such as high hardness, high thermal conductivity, and good breaking strength.
Non-European companies dominated the global Alexandrite laser crystal market, and only a Technology Readiness Level (TRL) of 4 could be attributed to the components available at the beginning of the project, i.e. validation in a laboratory environment.
The Horizon 2020 project GALACTIC - High Performance Alexandrite Crystals and Coatings for High Power Space Applications - aimed at pushing the Alexandrite laser crystal technology within the EU up to TRL 6 and establishing a fully European supply chain for high-quality, functionally coated Alexandrite laser crystals.
The project partners Optomaterials S.r.l. (Italy), Altechna (Lithuania), and Laser Zentrum Hannover e.V. (Germany, project coordinator) worked closely together to enhance the European state-of-the-art Alexandrite crystal and coating technology. Therefore, Optomaterials refined the crystal growth process and improved the machining and optical polishing quality. Altechna developed high-quality, low-loss, high laser-induced damage threshold coatings specifically tailored for Alexandrite. The Laser Zentrum Hannover designed, assembled and characterized two laser demonstrators, which mimic typical Earth observation laser source requirements, to assess the functional performance of the developed Alexandrite crystals. With the laser system operating in the low-energy, high repetition rate regime, a record output energy was demonstrated. An excellent lasing performance of the GALACTIC crystals and their competitiveness on the global market could be shown.
Finally, the GALACTIC consortium qualified the coated laser crystals to TRL 6 on component level via an environmental test campaign comprising thermal cycling as well as proton and gamma irradiation. No significant degradation of the optical parameters was observed after these tests.
Altogether, GALACTIC established a fully European supply chain for TRL 6 qualified Alexandrite laser crystals, enabled non-dependence of Europe on coated Alexandrite laser crystal technology and guaranteed its long-term European availability.
