ABSTRACT
A thin-film optical coating is a technique aimed at modifying in a well-established procedure, the surface properties that support it, and the application of the coating. Although the applied coating is expected to impart a host of numerous properties, environmental, thermal, chemical, and acoustical, the major purpose is often a plethora of expected specular optical properties that affect the quality of the light modified by the surface without changing its direction. To obtain such type of coatings, the surface has to be smooth in terms of its optical behavior that means that the deviations in size can be of order lesser than the wavelength of the incident light. The coatings may consist of one or more thin layers of desired materials that collectively present the properties that are desired ones, primarily due to a cumulative effect of interference and the innate properties of the chosen materials. At times the materials may themselves be engineered in terms of their micro-structure. The forces that are responsible for keeping together thin films and adhering them to their surfaces are of all short range order. However, these forces are very strong although of short range order and therefore a layer of contaminant one molecule thick can hinder the forces altogether. Thus both smooth and clean surface is the prerequisite for obtaining excellent surface coatings with desired specular optical properties.
