Magnetron sputtering devices rank among the most powerful coating apparatuses that are used to vapor deposit particles on the basis of plasma to produce high-quality interference filters of up to 200 mm in diameter and 40 mm in thickness. Thanks to the extremely stable growth of the layers, the excellent control of the layer thicknesses, the ability to apply multiple layers, for instance extremely hard and scratch-resistant AR coatings on sapphire substrates, and the high total thickness of the layer, extremely small band bandpass filters, steep edge filters or so-called notch filters (triple notch, for instance) are possible. These types of filters are used in the area of fluorescence microscopy or Raman spectroscopy.
With thermal evaporation onto cold substrates, the coating material is vapor deposited by the target (the coating material is referred to as the target) at a high temperature and condenses on top of the cold substrate as a thin layer. This method makes it possible to use the maximum number of various target materials (that have different refractive indexes), especially with low refractive materials with excellent transmission in the UV region. For this reason, this method is used for UV filters or for filters that require coatings with special refractive indexes.
With ion-assisted evaporation, the targets evaporated by an electron beam are also bombarded by ions rich in energy as they grow up on the substrate. By adjusting the ion beam, the properties of the layers can be modified to accommodate the refractive index or packing density of the coating.
With reactive ion plating, the metal target material is evaporated using an electron beam, plasma, and bombardment with ions and vapor deposited onto the substrate by adding a reactive gas as an oxidic layer (a TiO2 layer, for example). This technique achieves extremely dense layers that are exceptionally durable and thermally stable.