30.12.2021 • News

Space-qualified alexandrite laser crystals from Europe

To make the EU independent of non-European suppliers, Laser Zentrum Hannover (LZH), Altechna Coatings, and Optomaterials work on a purely European supply chain for space-qualified alexandrite laser crystals in the EU project Galactic.

Laser crystals made of alexandrite have a tunable wavelength between around 700 and 850 nanometers. When used in lidar systems in satellites, these crystals allow the determination of the chlorophyll content of the vegetation. This indicates the vegetation health and thus supplies valuable data, for example, for studies on climate change. In the EU project Galactic, the partners work on a purely European supply chain for space-qualified alexandrite laser crystals and on increasing their technology readiness level from TRL 4 to TRL 6.

Functionality test of the alexandrite crystals in the laser demonstrator...

LZH scientist Stefanie Unland sets up the laser demonstrator in the lab...

Laser systems for space must withstand strong temperature fluctuations as well as ionizing radiation. Therefore, Galactic optimizes crystal growth, purification, plasma pretreatment, and coating design to produce suitable alexandrite crystals.

The Italian partner Optomaterials has succeeded in growing alexandrite crystals of competitive quality. However, a particularly dense and resistant coating is required to make these crystals suitable for space applications. Altechna Coatings from Lithuania has therefore developed a special coating design based on the ion beam and magnetron sputtering process. In recent tests, the alexandrite crystals thus achieved a laser-induced damage threshold (LIDT) approaching top products on the world market.

The first of two laser demonstrators is already running in the development lab at LZH. “With well over 200 microjoules of pulse energy at a 5 kHz repetition rate, the demonstrator generates laser pulses that are a few nanoseconds short. Thus, in principle, this laser setup can scan large areas per time unit, which is an important prerequisite for the efficient operation of a lidar system,” reports Dr Peter Weßels, project coordinator and head of the solid-state lasers group in the LZH Laser development department.

In the third year of the project, the partners want to complete the tests and the comparative study, realize the second demonstrator and bring the manufacturing process to market maturity.