The study of lightning phenomena will be carried out by a dedicated instrument, the lightning imager, that will make use of narrow-band transmission filters for separating the Oxygen emission lines in the clouds, from the background signal. The design, manufacturing and testing of these optical filters will be described here.
The behaviour of interference optical filters for space applications has been investigated under low- and high-energy
proton irradiation. Low-energy protons are expected to be necessary to prove the effects on the coating, whereas the
high-energy proton tests shall verify mainly the substrate susceptibility to induced damage. The expected interaction of
protons with coating and substrate was simulated by software, to identify the most appropriate conditions for the
irradiation experiments. Two different accelerator facilities were used for low- and high- energy protons: 60 keV protons
with an integrated fluence of 1012 p+/cm2 and 30 MeV protons with an integrated fluence of 108 p+/cm2.
The spectral transmittance of the filters was measured before and after irradiation and, according to simulations, no
significant effects were detected in the visible-near infrared spectrum, while some variations appeared at short
wavelengths with low-energy irradiation.
Multilayer optical devices generally suffer from two main losses sources: absorption of the materials and scattering losses, due both to volume and surface effects. The exact estimation of this latter contribution is of extreme importance for the final assessment and optimization of efficient devices. In particular, when intrinsic absorption of the materials cannot be further reduced, scattering measurements may provide useful information for improving optical device performance.
In this work we investigated single SiO2, Al2O3 and HfO2 layers deposited by r.f. sputtering under different deposition conditions. These materials are being studied for implementation in multilayer dichroic mirrors for laser applications in the range from 260 to 350 nm. To avoid radiation damage, such devices need to be loss-free in the pumping and lasing region; hence, an insightful knowledge of all losses sources is fundamental.
Optical coatings for the use in free electron laser systems have to withstand high power laser radiation and the intense energetic background radiation of the synchrotron radiation source. In general, the bombardment with high energetic photons leads to irreversible changes and a discoloration of the specimen. For the development of appropriate optical coatings, the degradation mechanisms of available optical materials have to be characterized. In this contribution the
degradation mechanisms of single layer coatings (fluoride and oxide materials) and multilayer systems will be presented. Fluoride and oxide single layers were produced by thermal evaporation and high energetic ion beam sputter deposition. The same methods were employed for the deposition of multilayer systems. High reflecting coatings for the wavelength region around 180 nm were chosen for the irradiation tests. All samples were characterized after production by
spectrophotometry covering the VUV , VIS, and MIR spectral range. Mechanical coating stress was evaluated with interferometric methods. Synchrotron irradiation tests were performed at ELETTRA, using a standardized irradiation cycle for all tests. Ambient pressure and possible contamination in the vacuum environment were monitored by mass spectrometry. For comparison, the optical coatings were investigated again in the VUV, VIS, and MIR spectral range after irradiation. On selected samples XRD measurements were performed. The observed degradation mechanisms comprise severe damages like coating and substrate surface ablation. Color centre formation in the VIS spectral range and an increase of VUV absorption were found as a major origin for a severe degradation of VUV transmittance On the
basis of the performed investigations, a selection of coating materials and coating systems is possible in respect to the damage effects caused by synchrotron radiation.