With a high-refractive-index mixed-oxide dielectric material of ZrTiO(4) and ZrO(2) [Substance H2 (Sub2) from E. Merck, Darmstadt, Germany], in combination with magnesium flouride (MgF(2)), design optimization and experimental production of low-loss antireflection (AR) coatings are carried out. Design-optimization studies that make use of these materials as constituents of a seven-layer coating system demonstrate that when the useful bandwidth of an AR coating is extended to cover a wider spectral range, the designs are in general found to have increased integrated reflection loss, higher ripple, and increased spectral instability. The experimental studies on Sub2 material show that the films have excellent optical performance over a wider process window, the advantage of which is demonstrated in the production of different AR coatings on a variety of glasses with refractive indices that range from 1.45 to 1.784 and different mechanical, thermal, and chemical properties. The manufacturing process of AR coatings shows a consistency better than 99% with respect to optical properties and durability.
Keeping in view the importance of the development of antireflection coatings (ARC) on germanium (Ge) and silicon (Si) in the infrared region,suitable for terrestrial and space applications, the optical, thermal and mechanical properties of various semiconducting and dielectric materials are briefly reviewed. Cadmium telluride ,(CdTe) and zinc selenide (ZnSe) which are found to be the most suitable materials for ARC systems are deposited on Ge and their optical and non -optical properties are studied in detail. It is found that both these coatings enhance the transmission of Ge by 100 %.CdTe coatings in particular are found to withstand all severe environmental tests as per military specifications.
A dual stage, closed loop and self scanning algoritFin has been proposed for precise determination of optical constants i.e., refractive index, 'n', and absorption Index, 'k ' , together with thickness ' of thin film coatings . In the first stage , refractive index solutics over a knc.zn range are generated for a given set of nasured paranters , nanely, reflectance , R and trannittance , T, and preset thickness of the coating , where as in the seccd stage a merit function, defined in terms of mean square of the difference between refractive index values at consecutive wavelengths, is miriimised with respect to thickness. It is seen that while the algorithn can estimate the 'n ' , ' and ' d ' to an accuracy better than 0.005, 0.002 and 5/50 A0 (5 A0 for visible region coatings and 50 A0 for infrared coatings ) for an experinntal error of +0 . 005 in R arid T and it is able to overccme the ambiguity of ns.iltiple solutions, inherent in the existing methods.Apart from this, the required data can be generated faster, dispensing the cunbersane and expensive graphic systems. The algoritFin has been successfully appi ied to determine the optical constants of absorbing and transparent films.
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