European Commission logo
English English
CORDIS - EU research results

High Performance Alexandrite Crystals and Coatings for High Power Space Applications

Periodic Reporting for period 3 - GALACTIC (High Performance Alexandrite Crystals and Coatings for High Power Space Applications)

Reporting period: 2022-01-01 to 2023-04-30

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.
After the status evaluation of the European and non-European Alexandrite laser crystal and coating technologies, detailed specifications were deduced before starting the manufacturing process and the procurement of crystals from two leading non-European suppliers. The various growth runs performed within GALACTIC yielded crystals with reproducibly high quality. The characterization results showed the comparable if not better performance of the GALACTIC samples.
A review of relevant space missions enabled the compilation of a test plan for the TRL 6 qualification campaign. Besides, the international state-of-the-art of Alexandrite lasers was assessed to consolidate the requirements for two laser demonstrators set up at the Laser Zentrum Hannover. The first demonstrator in the cavity-dumped, q-switched operational mode (low energy, high repetition rate) was successfully assembled and optimized leading to record output parameters that by far exceed the target values. The setup and characterization of the second laser demonstrator (high energy, low repetition rate) was also completed, and the excellent lasing performance of the GALACTIC crystals could be verified in both systems.
Optomaterials researched the optimal growth conditions for high-quality crystals and thoroughly evaluated crystal structure data from X-ray diffraction and Raman measurements. They synthesized 16 boules using different growth parameters and achieved a sufficiently high doping concentration while maintaining the excellent optical quality. The large number of 228 shaped crystal components was extracted, machined, optically polished and comprehensively characterized.
Altechna processed the samples by various surface cleaning and etching methods and studied their influence on the surface characteristics and the durability against intense laser radiation via various characterization tests. In parallel, they designed two different coating systems which were realized and optimized in several coating runs. Thus, a significant enhancement of the laser-induced damage threshold (LIDT) could be achieved.
At last, the environmental test campaign could be successfully finished, leading to the final TRL 6 assessment of the GALACTIC components.
Much effort was spent on increasing the visibility of the project via a website, press releases and engagement in social media. The project and its outcome were presented at 11 scientific conferences and in the corresponding proceedings and peer-reviewed papers.
The European crystal grower and project partner Optomaterials could significantly improve the overall fabrication and characterization capabilities of the bulk material, whereas Altechna could enhance the crystal surface pre-treatment and coating processes. The Laser Zentrum Hannover could widen its knowledge and strengthen its position within the laser community by the development of laser systems based on Alexandrite with competitive or even record optical output parameters. Hence, the final functionally coated crystals did not only show the same quality as the ones from the non-European suppliers, but even surpassed them regarding relevant requirements for future space missions (e.g. LIDT).
The availability of TRL 6 space-qualified crystals is a worldwide unique feature of the components developed within the GALACTIC project. In addition, these high-quality, shaped and coated Alexandrite crystals were reproducibly manufactured solely by European suppliers.
The main impacts of the project’s results were to reduce the dependence on critical technologies and capabilities from outside Europe for future space applications. For the Alexandrite crystal and coating technology, this means even industrial independence due to the completely European supply chain. GALACTIC helped to develop or regain in the mid-term the European capacity to operate independently in space.
The use of functionally coated Alexandrite crystals is not restricted to laser systems for space missions. Another application is e.g. medical skin treatment. Since the partners are continuously looking for ways to improve the value chain of optical components, the GALACTIC results can be used to gain competitive advantage in various R&D-intensive markets of optics for high-energy laser systems.
To date, there are no Earth observation missions based on Alexandrite crystals. Different ESA-driven studies are undertaken, but all efforts rely on non-European technology, so far. The production of European high-performance, space-qualified Alexandrite crystals will simplify the design of such laser-based missions. The results of GALACTIC will push the development of space observation missions with optical payloads, which are a crucial building block in the understanding of our planet and its climate.
Alexandrite crystal boule
Alexandrite crystals as used in the GALACTIC project