Process monitoring is a must have for reliable and traceable production jobs. High-precision diagnostic optics have become a key technology in additive manufacturing online monitoring processes, where the interaction of the laser beam with the material will be observed and analysed. The applications require highest reflectivity and damage threshold, with lowest thermal drift. New dielectric-layer optical systems become more and more complex, optical interference coatings (OICs) have been gaining increasing importance for these optics. OICs are formed by a layer stack of alternating transparent single layers of high- and low-refractive-index material. A common method for manufacturing high-end coatings is plasma-ion-assisted deposition (PIAD), which is a combination of conventional electron-beam evaporation and a plasma assist source targeted directly at the surface of the substrates. Another coating technique is ion beam sputtering (IBS) coating. In IAD and IBS coatings the ion assisted coating process additionally allows the control of energy input (compared to E-beam/PVD coatings). This allows to produce ultra-dense coatings which are moisture free and are not sensitive to temperature changes. A comparison of the different coating techniques with new developed coatings for industrial use are discussed. The different techniques offer the possibility for spectral separation of processing/diagnostic wavelengths. No matter whether for OCT, pyrometer, thermo- camera or an observation in the visible wavelength range, the actual coating technique can be optimized for requirements of the application.