Fatigue, also known as optical component aging, is the gradual reduction in LIDT caused by a high number of laser pulses that are not powerful enough to cause initial laser damage. The duration of the laser pulse, as well as its wavelength, affects the resistance of the coating to laser-induced damage, especially at shorter pulse durations and lower wavelengths. This study’s aim was to evaluate dielectric IBS, IAD, and EB-coated UV mirrors operating in the single ps pulse regime and to define the key features that contribute to the aging of the component. For this purpose, laser-induced fatigue damage testing was completed at 343 nm wavelength using the S-on-1 procedure with single ps pulse duration by a laser system operating at a repetition rate of 200 kHz, with up to 10 million pulses per single site. LIDT values for two distinctive damage types were defined based on the observed changes in the sample: catastrophic failure and color-change modes. Subsequently, coatings with different spectral characteristics, surface properties and structural features were evaluated and their laser-induced fatigue damage results were compared.
A lot of investigations are ongoing for the development of laser systems with Alexandrite as active laser medium. These laser systems fulfill the general laser requirements for spaceborne Earth observation missions such as altimetry. However, to date, the laser systems and especially the coated Alexandrite crystals do not exceed Technology Readiness Level (TRL) 4. Therefore, the Horizon 2020 project GALACTIC was initiated to develop reproducible, fully European supplier-based functionally coated Alexandrite crystals, which show at least the same optical quality and laser performance in comparison to the components from the leading suppliers on the global market (mainly US and Chinese companies) and further fulfill the qualification to be generally used in space (i.e. verification of TRL 6). We present the high optical quality and good laser performance results of our developed Alexandrite crystals tested in a cavity-dumped Q-switched laser system. Furthermore, we show on the one hand the reproducibility and on the other hand the competitiveness of our crystals by a comparison study with our GALACTIC samples and crystals from two non-European suppliers. Additional presentation content can be accessed on the supplemental content page.
Despite the extensive studies of Alexandrite as a potential laser-active medium for future Earth observation space missions in the last years, the corresponding laser systems and especially coated Alexandrite crystals do not exceed Technology Readiness Level (TRL) 4. This means that although the developed Alexandrite-based laser systems have been validated in the laboratory, it has not been published up to now, whether they can withstand the harsh environmental conditions in space. In the course of the Horizon 2020 project GALACTIC, high-quality functionallycoated Alexandrite crystals developed and manufactured within the GALACTIC project will be qualified according to TRL 6 in an environmental test campaign comprising irradiation and thermal cycling tests together with optical performance tests before and afterwards (functional laser tests, LIDT, and transmission measurements). In this work, we present our strategy for testing functionally coated alexandrite crystals for space applications developed, fabricated and tested in a fully European supply chain within the GALACTIC project with the goal of increasing the TRL level to 6.
Modern laser systems have paved the way for spaceborne laser applications such as Earth's surface and atmosphere monitoring. Well known technologies like Nd:YAG lasers are often employed; however, they do not always comply with all the different requirements for space missions. High optical efficiencies and tunable wavelength, which are desirable for many applications, can be reconciled with a simple laser design employing Alexandrite crystals. Horizon 2020 project presented here discuss the results on the development of alexandrite laser crystal treatment prior to coating deposition, as well as future plans on crystal interference coating deposition for LIDT improvement.
Spaceborne Earth observation based on laser instruments provides new technologies to monitor the atmosphere or our planet’s surface. Space-qualified Alexandrite laser crystals show convincing properties as a laser-active medium in high power laser systems for space-based missions, e.g. the wavelength tunability and the excellent material properties, such as high thermal conductivity and a good breaking strength. Therefore, the Horizon 2020 project GALACTIC was initiated to realize space-qualified, high-quality coated Alexandrite crystals relying on a purely European-based supply chain. The project consortium will push the development of Alexandrite crystals and coatings within the EU from the current Technology Readiness Level (TRL) 4 up to TRL 6. The Horizon 2020 project GALACTIC, which will be presented, has been initiated to realize space qualified high quality, high performance coated Alexandrite crystals rest on a purely European-based supply chain. The project consortium, consisting of Optomaterials S.r.l., Altechna Coatings and the Laser Zentrum Hannover e.V., provides the necessary expertise in the fields of laser crystal growth, optical coatings and laser systems to push the development of high quality, high damage threshold Alexandrite coatings within the EU up to TRL 6. In order to reach the GALACTIC goals, different technology areas will be addressed. On the one hand, Optomaterials S.r.l. as an experienced optical crystal manufacturer will continuously refine the crystal growth process and improve the raw crystals as well as the cutting and polishing quality step-by-step. As an experienced company in optical coatings production for space applications, Altechna Coatings will secondly develop high quality, low loss, high damage threshold coatings specifically tailored for application onto Alexandrite laser crystals. The superior performance of the coated crystals will then be proven in demonstrator laser systems. The Laser Zentrum Hannover e.V. has the required knowledge to set up laser demonstrator prototypes, whose specifications mimic typical earth observation laser source requirements. Finally, the GALACTIC consortium will work closely together to characterize and qualify the developed coated laser crystals. By collaborating with the European space industry and deriving the detailed requirements from typical earth observation space missions, a detailed TRL 6 components test plan will prove the TRL 6 qualification of the developed coated laser crystals. This will conclude the development process and will enhance the European non-dependence status of the Alexandrite laser crystal market. At the conference, we will present the project and its consortium as well as detailed strategies to enable a non-dependence of Europe on coated Alexandrite laser crystal technology and enabling long term European availability of this technology. This project has received funding from the European Union's Horizon 2020 research and innovation programme under Grant Agreement No 870427.
KEYWORDS: Crystals, Laser crystals, Alexandrite lasers, Alexandrite, Space operations, Laser systems engineering, Laser applications, New and emerging technologies, Manufacturing, Laser development
Alexandrite is a promising, highly efficient laser material enabling wavelength tunability for applications in the field of spaceborne Earth observation. The Horizon 2020 project GALACTIC has been initiated to establish a fully Europeanbased supply chain for high-quality functionally coated Alexandrite laser crystals. To reach this goal, the project consortium, consisting of Optomaterials S.r.l., Altechna Coatings and the Laser Zentrum Hannover e.V., works closely together to firstly develop and improve the crystal manufacturing and coating technologies and secondly to characterize the developed coated laser crystals. Finally, the Technology Readiness Level (TRL) of 6 will be achieved for typical Earth observation space missions. The necessary qualification test campaign will conclude the development process and will enable European non-dependence from the Alexandrite laser crystal market currently dominated by non-European suppliers.
The development of advanced laser systems has paved the way for spaceborne laser applications like Earth’s atmosphere and surface monitoring. Prominent technologies like Nd:YAG are often exploited, however they have proven a challenge to combine the different requirements for space missions. High optical efficiencies and tunable wavelength, which are desirable for many applications, can be reconciled with a simple laser design employing Alexandrite crystals. Horizon 2020 project presented here focuses on the development of high quality and high performance coated Alexandrite crystals along with the construction of a laboratory prototype Alexandrite laser system with specifications suitable for Earth observation missions.
A novel approach for efficient manufacturing of three-dimensional (3D) microstructured scaffolds designed for cell studies and tissue engineering applications is presented. A thermal extrusion (fused filament fabrication) 3D printer is employed as a simple and low-cost tabletop device enabling rapid materialization of CAD models out of biocompatible and biodegradable polylactic acid (PLA). Here it was used to produce cm- scale microporous (pore size varying from 100 to 400 µm) scaffolds. The fabricated objects were further laser processed in a direct laser writing (DLW) subtractive (ablation) and additive (lithography) manners. The first approach enables precise surface modification by creating micro-craters, holes and grooves thus increasing the surface roughness. An alternative way is to immerse the 3D PLA scaffold in a monomer solution and use the same DLW setup to refine its inner structure by fabricating dots, lines or a fine mesh on top as well as inside the pores of previously produced scaffolds. The DLW technique is empowered by ultrafast lasers - it allows 3D structuring with high spatial resolution in a great variety of photosensitive materials. Structure geometry on macro- to micro- scales could be finely tuned by combining these two fabrication techniques. Such artificial 3D substrates could be used for cell growth or as biocompatible-biodegradable implants. This combination of distinct material processing techniques enables rapid fabrication of diverse functional micro- featured and integrated devices. Hopefully, the proposed approach will find numerous applications in the field of ms, microfluidics, microoptics and many others.
We present a novel approach to manufacturing 3D microstructured composite scaffolds for tissue engineering applications. A thermal extrusion 3D printer – a simple, low-cost tabletop device enabling rapid materialization of CAD models in plastics – was used to produce cm-scale microporous scaffolds out of polylactic acid (PLA). The fabricated objects were subsequently immersed in a photosensitive monomer solution and direct laser writing technique (DLW) was used to refine its inner structure by fabricating a fine mesh inside the previously produced scaffold. In addition, a composite material structure out of four different materials fabricated via DLW is presented. This technique, empowered by ultrafast lasers allows 3D structuring with high spatial resolution in a great variety of photosensitive materials. A composite scaffold made of distinct materials and periodicities is acquired after the development process used to wash out non-linked monomers. Another way to modify the 3D printed PLA surfaces was also demonstrated - ablation with femtosecond laser beam. Structure geometry on macro- to micro- scales could be finely tuned by combining these fabrication techniques. Such artificial 3D substrates could be used for cell growth or as biocompatible-biodegradable implants. To our best knowledge, this is the first experimental demonstration showing the creation of composite 3D scaffolds using convenient 3D printing combined with DLW. This combination of distinct material processing techniques enables rapid fabrication of diverse functional micro-featured and integrated devices. Hopefully, the proposed approach will find numerous applications in the field of tissue engineering, as well as in microelectromechanical systems, microfluidics, microoptics and others.
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