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Lineare und nichtlineare Interferometrie zur Präzisionsvermessung von Mikrostrukturen

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This diploma thesis deals with interferometric measurement methods which are employed to determine the microstructure of objects. In the first part an interferometric measuring tool was designed to investigate the dispersion properties of laser mirrors, which are strongly dependent on the mirror structure. The phase was retrieved from the spectrally-detected interferogram to evaluate the wavelength dependent group delay dispersion by double differentiation. Secondly a setup for linear Optical Coherence Tomography (OCT) was built using a 5-fslaser with very broad bandwidth as a light source. This technique allows direct imaging of micrometer-scale structures. Discontinuities of the refractive index are detected in an interferometric setup, in which the axial resolution is determined by the coherence length of the light source used. However, linear OCT is not sensitive to the reflecting material itself. This can be achieved by using Second Harmonic Optical Coherence Tomography, where the frequency-doubled light from the sample is interfering. Therefore, in the third part the OCT-setup was upgraded to allow ultrahigh-resolution Second Harmonic OCT with a resolution of 6.5 µm.

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