Computational experiments on optical coating production using monochromatic monitoring strategy aimed at eliminating a cumulative effect of thickness errors

We present an algorithm for the automatic generation of a monitoring spreadsheet that enables the most effective application of the termination level correction algorithm proposed in our previous publication. On a whole the presented monochromatic monitoring strategy entirely eliminates a cumulative effect of thickness errors in optical coating production using direct optical monitoring. The effectiveness of the new monitoring strategy is demonstrated by computational manufacturing experiments in which such error factors as instability of deposition rates, errors in measured transmittance data, shutter delays, and variations of layer refractive indices from their theoretical values are simulated.     

Elimination of cumulative effect of thickness errors in monochromatic monitoring of optical coating production: theory

We propose an algorithm for correcting deposition termination levels that allows elimination of the cumulative effect of errors in previously deposited layers. For the application of this algorithm at least one monitoring signal extremum should be registered during a layer deposition. We also derive a theoretical relation for the estimation of errors in layer refractive indices based on the results of on-line monitoring measurements. At least two monitoring signal extrema are required for its application.     

Investigation of the effect of accumulation of thickness errors in optical coating production by broadband optical monitoring

We present a theoretical approach enabling one to perform a preproduction investigation of the effect of accumulation of thickness errors in the course of optical coating production using broadband optical monitoring. On the basis of this approach we investigate and compare thickness errors that may be associated with such factors as random and systematic errors in measurement data, instabilities of deposition rates, and inaccuracies of on-line algorithms predicting termination instants for layer depositions.     

Double optical monitoring of dip coating with a time-varying refractive index

A brief overview of optical monitoring for vacuum and wet-bench film-deposition processes is presented. Interferometric and polarimetric measurements are combined with regard to simultaneous monitoring of refractive index and physical thickness in real time. Monitoring stability and accuracy are verified during dip coating with a transparent oil standard. This double optical technique is applied to dip coating with a multicomponent zirconyl chloride aqueous solution, whose resulting temporal refractive-index and physical-thickness curves indicate good reproducibility as well as significant sensitivity to changes of film-flow properties during the dip-coating process.     

Analysis of dip coating processing parameters by double optical monitoring

Double optical monitoring is applied to determine the influence of main process parameters on the formation of sulfated zirconia and self-assembled mesoporous silica solgel films by dip coating. In addition, we analyze, for the first time to the best of our knowledge, the influence of withdrawal speed, temperature, and relative humidity on refractive-index and physical thickness variations (uncertainties of +/-0.005 and +/-7 nm) during the process. Results provide insight into controlled production of single and multilayer films from complex fluids by dip coating.     

Estimations of production yields for selection of a practical optimal optical coating design

Modern design approaches enable one to construct a series of theoretical designs with excellent spectral properties for almost all optical coating design problems. Selection of a practical optimal design among a variety of possible theoretical designs becomes a key issue. We demonstrate how preproduction estimations of expected production yields can be used for selection of a practical optimal design. The question of reliability of such estimations is also addressed.     

Statistical approaches to groundwater monitoring

Current and proposed regulations require that some form of Student's t-test be used for evaluation of groundwater pollution detection parameters. Several problems arising from that requirement lead to an inflated false alarm rate. Among these are the use of variability among replicates as the estimate of random sampling error, and the failure to take proper account of spatial and temporal sources of variation. In addition, conditions essential for the valid application of the t-test are usually lacking. The requirement that a separate t-test be conducted for each detection parameter, each reporting period, causes an additional severe increase in the likelihood of a false alarm. A dummy variable analysis of covariance is suggested as a desirable alternative. After statistically removing temporal variation from the data the averages of the upgradient and downgradient wells are compared. Examples of the use of this form of analysis are given.     

Optical parameters of oxide films typically used in optical coating production

Wavelength dependencies of refractive indices of thin film materials differ for various deposition conditions, and it is practically impossible to attribute a single refractive index wavelength dependence to any typical thin film material. Besides objective reasons, differences in the optical parameters of thin films may also be connected with nonadequate choices of models and algorithms used for the processing of measurement data. The main goal of this paper is to present reliable wavelength dependencies of refractive indices of the most widely used slightly absorbing oxide thin film materials. These dependencies can be used by other researchers for comparison and verification of their own characterization results.     

Statistical approach to brittle fracture

A general expression for the failure probability of a brittle material is developed by using the properties of flaw size distribution and the stress necessary to fracture an inclined crack. A comparison is made with Weibull analysis and an expression for the Weibull modulus, which is known to be an empirical material constant, is related to the properties of the flaw size distribution of a material. Limitations in the application of Weibull analysis are also discussed.     

Statistical process control via context modeling of finite-state processes: an application to production monitoring

Conventional Statistical Process Control (SPC) schemes fail to monitor nonlinear and finite-state processes that often result from feedback-controlled processes. SPC methods that are designed to monitor autocorrelated processes usually assume a known model (often an ARIMA) that might poorly describe the real process. In this paper, we present a novel SPC methodology based on context modeling of finite-state processes. The method utilizes a series of context-tree models to estimate the conditional distribution of the process output given the context of previous observations. The Kullback-Leibler divergence statistic is derived to indicate significant changes in the trees along the process. The method is implemented in a simulated flexible manufacturing system in order to detect significant changes in its production mix ratio output.     

Equivalence of pyrheliometric and monochromatic aerosol optical depths at a single key wavelength

The atmospheric aerosol optical depth (AOD) weighted over the solar spectrum is equal to the monochromatic AOD at a certain wavelength. This key wavelength is ~0.7 mum, which is only slightly influenced by air mass and aerosol content. On the basis of this result, simple relations are proposed to predict monochromatic AOD from pyrheliometric data and vice versa. The accuracy achieved is close to ?0.01 units of AOD at ~0.7 mum, estimated from simultaneous sunphotometer data. The precision required for the estimation of the precipitable water-vapor content is approximately ?0.5 cm.     

Statistical approach to roughness-induced shielding effects

A new theoretical concept is introduced to describe the roughness‐induced shielding effects in metallic materials. This approach is based on the statistics of the local ratio between the characteristic microstuctural distance and the plastic zone size. A general equation involving both the crack branching and the crack closure phenomena is derived in the frame of linear elastic fracture mechanics under the assumption of remote mode I loading. It enables the determination of the intrinsic values of both the fracture toughness and the fatigue crack growth threshold. Moreover, the roughness‐induced component can be separated from other closure components, such as the plasticity or oxide‐induced closure. In order to estimate the total roughness‐induced shielding effect only standard materials data such as the yield stress, the mean grain size, the surface roughness and the fracture mode are necessary. Examples of applications concerning static fracture and fatigue are presented for selected metallic materials.     

Impedance spectroscopy monitoring of a polyurethane coating on mortar exposed to NaCl solution

Polyurethane coated OPC mortar specimens exposed to 1M NaCl solution were studied by impedance spectroscopy and SEM over a period of 4 years. Results showed a rapid reduction of the coating resistance over the first half year, followed by a slow decrease thereafter. The coating deteriorated starting from the surface in contact with the NaCl solution and the deterioration front reached the coating/substrate interface after around three years. Different stages of deterioration were clearly identified by impedance spectroscopy. The study demonstrates that impedance spectroscopy is a versatile and informative non-destructive method to assess and monitor the performance of surface treatments on concrete.     

Interferometric monitoring of dip coating

Dip-coated films, which are widely used in the coating industry, are usually measured by capacitive methods with micrometric precision. For the first time to our knowledge, we have applied an interferometric determination of the evolution of thickness in real time to nonvolatile Newtonian mineral oils with several viscosities and distinct dip withdrawing speeds. The evolution of film thickness during the process depends on time as t(-1/2), in accordance with a simple model. Comparison with measured results with an uncertainty of +/- 0.007 microm) showed good agreement after the initial steps of the process had been completed.     

Agro-residues for enhanced production of bio-colorants: a feasible approach for dyeing and surface coating of leather

Clean Technologies and Environmental Policy - There is a growing demand for eco-friendly and non-toxic dyes that can be used to impart color to a wide variety of materials. Synthetic dyes are known...     

Statistical approach to time-dependent failure of brittle material

In a previous paper [1], the failure of brittle material due to slow crack growth under constant loading condition was analyzed by combining the theory of stochastic process and the extreme value distribution of crack length. In the present paper, the statistical treatment in the previous paper is improved and extended to predict the time-dependent probabilities of fracture and fracture location of brittle materials under dynamic loading condition. Experimental confirmation of the analytical method is obtained using soda-lime glass in water as the model material environmental system.     

Statistical approach to delayed failure of brittle materials

Delayed failure tests or static fatigue tests were performed on soda-lime glass in water environment. Testing consisted of four-point bend and three-point bend with constant load. The time-to-failure and fracture location of specimens were measured.The theory of stochastic process is combined with the extreme value distribution in stress and the time dependent probability distribution function is obtained to predict the time-to-failure of specimens as well as the location of fracture.It is shown that the theoretical prediction is in good agreement with the experimental data.

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Résumé Des essais de rupture différée ou essais de fatigue statique ont été exécutés sur un verre calcique sodé dans un environnement d'eau. Les essais consistaient en une flexion en quatre points et en une flexion en trois points à charge constante. On a mesuré le temps à la rupture et la localisation de la rupture sur les éprouvettes.En combinant la théorie du processus stochastique avec la distribution aux valeurs extrèmes de la contrainte et de la fonction de distribution de la probabilité de rupture en fonction du temps, on a pu prédire le temps à la rupture des éprouvettes ainsi que la localisation de la rupture.On montre que la prédiction théorique est en bon accord avec les données expérimentales.

     

Diffractive optical elements for beam shaping of monochromatic spatially incoherent light

Fresnel-type diffractive optical elements (DOEs) for general beam shaping of monochromatic, spatially incoherent light are demonstrated. Direct and indirect methods, i.e., adding a lens' phase to the designed Fraunhofer-type DOEs, are used for the design. The indirect method can reduce the calculation time by approximately half without loss of design accuracy. Two different design examples are shown. For one design the direct method gives a maximum sidelobe intensity of 5.0% of the maximum intensity in the signal window. For the second design the indirect method gives 23.0% of this value. The generated patterns can maintain their basic shapes over a long distance. The elements have been fabricated by directly using gray-scale commercial slides as masks. Experimental results are in close agreement with numerical predictions.     

Path of a beam of light through an optical coating

A simple model for the path of a light beam through an optical coating is the path of a ray predicted by Snell's law. By determining the exit point of a beam for various types of coating, one finds that the simple model is a good approximation in the case of antireflection coatings, but not for coatings of other designs. An approximate method for determining the correct path of a beam through the coating is derived and the path is illustrated using a Gaussian incident beam and tracing the position of the peak field of the beam as it traverses the coating.     

Statistical monitoring and control of a low defect process

Advanced technologies today are such that it is possible to keep the occurrence of defects in manufactured products at very low levels. The use of the conventional c-chart for statistical control of defects in such products would encounter serious practical difficulties because the low defect counts would render invalid the theoretical assumptions used in the construction of the chart. Based on reasoning with fundamental probability distributions, this paper offers a simple and reliable solution that is particularly suited to on-line inspection and testing operations such as those found in an automated manufacturing environment.