Ion assisted deposition with low-energy ions for applications in modern optics

Main objective of this work is the development of ion assisted deposition processes without additional substrate heating for applications in precision and laser optics. New low-energy ion sources with ion energies below 100 eV were employed for the research work. Starting point of the process development are basic investigations on the ion assisted evaporation of fluoride and oxide thin film materials. The optimisation of the coating processes is primary done with the help of optical characterisation methods (spectral photometry, laser calorimetry, measurement of the total scattering). For the fluoride materials it has been possible to minimise the preferential sputtering effects, which are combined with absorptive losses caused by stoichiometric degradation, using low-energy xenon ions. The properties of ion assisted oxide films can be scaled with the deposited ion energy per condensing thin film molecule. The refraction index and the packing density increase with this energy, simultaneously the absorption of the thin film is reduced and the absorption edge comes close to the corresponding bulk value. Compared to conventionally deposited films the packing density is increased and the absorption, the water content and the scattering is reduced. The extinction coefficients at a wavelength of 532 nm lie below 5.10-5. The results of the investigations on single films are employed for the production of wideband antireflective coatings. Coatings on PMMA can be realised by a process adaptation with UV-absorbing films. A further focal point are antireflective coatings on alkali halides optics for high-power CO2-lasers. Ion assisted deposition of NaF-films at extremely low ion energies (Eion∼5 eV) qualifies antireflective coatings with minimal absorption (α∼1.5 cm-1), high short-pulse damage threshold (50%-LIDT∼60J/cm2) and improved degradational stability