In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: a b s t r a c t a r t i c l e i n f o We present extended experimental material about optical and mechanical properties of oxide optical coating materials, deposited by electron beam evaporation, ion and plasma ion assisted evaporation, sputtering and ion plating. A clear correlation between these experimental data is established and understood as being caused by the different degree of the porosity of the films. This assumption has been verified by investigation of the layer structure and accompanying simulations of the effect of porosity on refractive index, layer stress and thermal shift. As a practical conclusion, we find that a certain pore fraction in the films is essential in order to get a valuable balance between optical and mechanical coating properties. It is well known, that the performance of optical coatings crucially depends on the production accuracy and reproducibility of geometrical coating parameters such as film thickness, surface smoothness, defect (pinhole) concentration and the like. On the other hand, excellent, environmentally stable and reproducible values of optical thin film material constants like refractive indices and small extinction coefficients are required as well. Ideally, the films should not have gradients of optical properties, and their refractive index and extinction coefficient should be independent of the film thickness. Therefore, formation of amorphous layers is favoured. Additional requirements on non-optical material properties like small mechanical stress are equally important [1–3]. From thin film theory it is well known, that for any spectral target defined at normal incidence and practically non-absorbing materials, the optimal design is achieved with a pair of materials that reveal a refractive index contrast as high as possible [4]. As a consequence of this general design recipe, there arises a need to optimize deposition techniques and conditions with the goal to maximize achievable refractive indices of traditional high-index materials. In modern ion assisted versions of optical coating techniques, the high densification of the coating leads to film refractive indices close to or higher than reported bulk values [2]. Hereby the ion plating techniques and reactively pulsed magnetron sputtering are reported to deliver coatings with the highest refractive indices known today [5]. As …

We present extended experimental material about optical and mechanical properties of oxide optical coating materials, deposited by electron beam evaporation, ion and plasma ion assisted evaporation, sputtering and ion plating. A clear correlation between these experimental data is established and understood as being caused by the different degree of the porosity of the films. This assumption has been verified by investigation of the layer structure and accompanying simulations of the effect of porosity on refractive index, layer stress and thermal shift. As a practical conclusion, we find that a certain pore fraction in the films is essential in order to get a valuable balance between optical and mechanical coating properties.

Stochastic, self-organized nanostructures are produced by a low-pressure plasma treatment on the polymer polymethylmetacrylate (PMMA). The phenomena obtained by plasma treatment (structure formation and antireflective effect) are investigated regarding surface modifications, structure growth, and chemical modifications. Optically, the structure acts like a gradient layer with decreasing effective refractive index towards air, which is suitable for antireflection of PMMA.

The application of plasma treatment on transparent PMMA substrates has shown an effect of reducing surface reflection. This effect is based on a refractive index gradient created by a combination of chemical decomposition and physical etching on the polymer surface. A stochastic nanostructure was found by means of AFM and SEM. Conditions for the plasma treatment process and properties of the modified PMMA surfaces have been discussed.