The AEI 10 m prototype will be an ultra-low displacement noise facility consisting of an L-shaped ultra-high vacuum system with about 10 m long arms, excellent seismic isolation, a well-stabilized high power laser and other advanced interferometry techniques. In the first round of experiments an interferometer to measure at the standard quantum limit of classical interferometry will be set up. This paper describes the status of the AEI 10 m prototype and its individual sub-systems as of April 2012.
In order to enhance the reliability and performance of space-based Lidar systems, it is desirable to increase the damage resistance of ultraviolet antireflective coatings. For laser pulses with nanosecond pulse duration, laser-induced damage is known to be triggered by nano-sized defects embedded in the optical coating. In this work, we demonstrate the mitigation of damage precursors during the manufacturing of ion-beam sputtered (IBS) coatings using two approaches: ion bombardment with a secondary ion source and laser irradiation with a nanosecond-pulsed laser. Optical coatings produced with both technologies show a significantly increased damage threshold when tested in large-area raster scans.
An approach for the measurement of the laser-induced damage threshold with two wavelengths combined was made while testing antireflective coatings for the wavelengths 266 and 532 nm. Samples were made of Al2O3/SiO2 and HfO2/SiO2 ion beam sputtered films. The results show that adding radiation of a second wavelength might lead to a significant reduction of the threshold. The damage morphology of single and dual wavelength tests is very similar and does not suggest an altered damage mechanism. Further investigations indicated that the dual wavelength threshold is a function of the temporal delay of the two pulses.
IBS Coatings are a good candidate for high performance applications. They are hard, dense, exhibit a small thermal shift, and have the best scattering and surface roughness performance of the various coating technologies. In addition, they feature a highly stable refractive index for the coated materials allowing the production of complex coatings. Because of their high density and resistance towards high energy radiation IBS coatings are also well suited for space applications. For high power laser applications, the vacuum stable damage threshold and low defect concentration qualify especially reactive ion beam sputtering as a suitable deposition method for space applications. In the paper, results on coating activities using the IBS process are discussed in respect to two aspects. One is the adaption of the IBS to strongly curved surfaces like lenses exemplified by the FM lenses for the Copernicus Sentinel-4 mission. The other is a study to increase the laser-induced damage threshold for future LIDAR systems. This is accomplished by eliminating nano-scaled particles that act as damage precursors during laser radiation.
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