Andrushchak N. Development of methods and tools for determining refractive indices of optoelectronic elements in the wavelength range 400nm-10mm

The dissertation is dedicated to creation and test of experimental methods and tools for precise express-measurements of refractive indices of plane-parallel or wedge-shaped elements of optoelectronic devices in the range from visible light to millimeter waves. Different types of experimental setups are created. For these setups, special measuring methods are developed and precise working formulas are derived that take into account the refractive properties of air as the environment in which a sample is located, as well as deviations of surfaces of that sample from parallelism. The regularities for changes in the optical path are found, which appear due to the inevitable uncontrolled non-parallel surfaces or planned wedge-shaped samples. The analytical expressions for calculating refractive indices of isotropic and anisotropic materials are derived, allowing to get rid of the corresponding systematic errors. The errors for the refractive index determination in different spectral ranges are evaluated both theoretically and experimentally. A simplified interferometric method for measuring refractive indices of optoelectronic elements in sub-Terahertz range (50-500 GHz) is developed. This method is to build an interference minimum in the memory of vector network analyzer due to a linear shift of the electromagnetic radiation receiver, with subsequent measurement of this minimum shift by introducing a sample under test into the working channel, thus allowing to get rid of the reference channel and simplify the measurement process. The novel method for simplified measurements of refractive indices in the sub-Terahertz range is testified experimentally and the data obtained show a good agreement when compared to the literature data. A software complex is developed allowing to control experiment procedures and data processing in the frame of modern engineering environment LabVIEW which uses the equipment from "National Instruments". Computer-controlled experiments carried out by us demonstrate both high accuracy of the measurements (4-5 and 2-3 decimal digits after period for the visible and millimeter wavelength ranges, respectively) and a possibility for express-analysis of optoelectronic elements under test (the time of a single measurement cycle not exceeding 5 min.).The methods and tools developed here make it possible to perform non-destructive determination of the refractive indices for plane-parallel and wedge-shaped isotropic and anisotropic optoelectronic elements that are suitable for further usage in specific applications. For the first time the refractive indices of an optical glass, a crystalline quartz, sapphire and an evlitine are determined in the millimeter-wave range. Furthermore, the values of the refractive indices of lithium niobate crystals and quartz are determined more precisely in the visible range. The databases of parameters of optoelectronic materials are enriched by the results obtained using the developed methods and tools.