RESUMEN
Optical monitoring of periodic thin-film stacks by the termination of each layer at the same constant photometric level has certain advantages. One of these principal advantages is the error compensation effect in the vicinity of the monitoring wavelength. In this study, we examine, by simulation, the effect of an error in the knowledge of the absolute value of the photometric termination level on the probable stability in the manufacture of the edge position of a blocked band. The results include equations that allow the determination of the appropriate values of parameters associated with the optimum termination levels to minimize the effects of such errors.
RESUMEN
Empirically derived formulas are given that allow the thin-film designer to estimate in advance the number of layers needed to meet various thin-film optical performance requirements. The estimation of peak optical density and width of higher-order blocker bands and their suppression are also discussed.
RESUMEN
The most common approaches to the application of the Fourier transform method to the synthesis of thin films suffer from two difficulties. The function of reflectance or transmittance to be transformed has been variously approximated, but none of the approximations has been recognized as giving accurate results for all cases. The transformed results for high-reflectance cases have what appear to be distortions in the frequency and in the amplitude scales. These problems and their solutions are the subjects of this paper. It is shown that the reflectance amplitude is the function that should be transformed and that the inclusion of multiple reflections eliminates the distortions in frequency and amplitude.
RESUMEN
An empirically derived formula, which can be used to predict the average residual reflection that can be expected from an antireflection (AR) coating design as a function of bandwidth, overall thickness, available indices of the coating materials, number of layers, etc., is presented. This formula can be a useful tool not only for the thin-film designer but also for the nondesigner or system engineer to estimate the performance limits of an AR coating for a given application before the design is accomplished. The general predictions are also found to be consistent with the results of two recent AR design competitions involving many independent investigators. Some insight with respect to the basic underlying principles of AR coatings can also be gleaned from the results and the process by which they are found.
RESUMEN
An iterative correction process, recently incorporated into the National Research Council of Canada Fourier-transform thin-film synthesis program, is applied to the design of wideband antireflection coatings. This type of problem is different from those solved in the past by this method. It cannot be handled in a practical way without a correction process. We consider in detail the effects-critical for this application-of constraints on the refractive indices and overall thicknesses of the solutions. Our graded-index and multilayer designs have a remarkable resemblance in performance and refractive-index structure to results obtained by more conventional techniques. The Fourier-transform method is of interest because of its speed and versatility.
RESUMEN
Uncoated surfaces of high index glasses when cemented to form lens doublets have inferior antireflection properties to doublets of low index glass. This can be overcome by the application of a single layer coating of aluminum oxide prior to cementing.
RESUMEN
We show the principles of Herpin index and Epstein equivalent period approximations in graphic form and discuss the possibilities and limitations of the approximations with changes in wavelength and angle of incidence.
RESUMEN
Semidirect level monitoring has error compensation capabilities of potential benefit to optical coatings of certain types. A review of the principles of level monitoring using circle diagrams shows how to design a level monitoring scheme for various cases, including the use of precoated monitoring chips. The film thickness sensitivities for various optical monitoring strategies differ considerably. Optimum level trigger point monitoring offers improved sensitivity of change in reflectance vs change in optical thickness. This procedure is also expected to give small thickness errors when optically monitored. Optimum level trigger point monitoring, and its application, is fully described.