GCRIS

This thesis presents studies of the defect centers in hBN and design of nonlinear waveguide. The multilayer hBN flakes and Si3N4 waveguide are available materials in modern nanophotonics applications. The color centers in hBN are consisted of quantized states because each defect center has different saturation power and dipole polarization. The line shape of emission from defect centers is directly depended photon vibrations and temperature of sample. Moreover, phonon bands in the color centers affect the wavelength of emission and we statistically worked on the phonon effects on ZPL. The Si3N4 waveguide can be more efficient chip scale photon pair sources to create entangled photons in visible band. The zero dispersion wavelength calculations give an efficient waveguide geometry as 650×600 nm2 for 780 nm pump wavelength.

Interface acoustic waves can propagate in solid-solid and solid-liquid interfaces. They are perturbed by ambient conditions, interface materials and characteristics. The wave energy are shared between two interfacing media, with its distribution depending on these properties. In this study, it was aimed to make liquid characterization (density) using interface acoustic waves. The waves propagating between the plate and the liquid interface are kind of flexural waves and known as quasi-Scholte mode. Firstly, the wave propagation for multilayered system is analytically modelled. A global matrix method is employed for obtaining the dispersion characteristics of the multilayer structure by considering the boundary conditions of the system. In order to develop the dipstick sensor, liquid characterization is performed firstly by test cell method for longitudinal bulk velocity of the liquid with known density. Test cells with two different lengths were used for measurements. In this technique, transmitting and receiving transducers are placed on opposite sides of test cell. Based on the distance between transducers and time of flight, velocity of longitudinal bulk waves was calculated. Mixtures of ethanol-pure water were prepared at various ratios and measurements were taken at different temperatures. Quasi-Scholte mode dipstick sensoring is employed by a simple measurement waveguide or dipstick inserted into the fluid to measure the velocity of the quasi-Scholte mode on a plate. This method, is based on mode conversions of waves. When the shear wave is excited on the aluminum plate, which is used as dipstick, Lamb waves occur at the solid-gas surface. The lamb waves are then converted into different modes in the solidliquid interface. Leaky Rayleigh and Scholte propagating modes exist in immersed part as well. Quasi-Scholte wave propagate on the interface while the Leaky Rayleigh modes lose their energy. By means of dipstick method, alcohol water mixtures which is used in test cell method, were measured at room temperature. The signals obtained as a result of the experiments were processed by the zero phase slope method. Time delay between reflected signals are found from phase slopes of the signals.

Master Degree / Yüksek Lisans Tezleri

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