Two-photon modification of materials with ultrashort laser radiation : Z-scan measurements and 3D-modification of selected materials

Abstract

This dissertation consists of three interrelated parts; analytical calculations, numerical calculation and experimental measurements. In the analytical calculation part, the property of a Gaussian laser beam has been first reviewed. Then, it has been described how a Gaussian beam propagates through free space using Fresnel approximation and Fraunhofer diffraction theory. In the open aperture Z-scan the entire energy transmitted through the nonlinear medium is collected. The normalized transmittance assuming the following different order of nonlinearity has been calculated: 2PA as a third order nonlinear absorption using a circular Gaussian beam, 2PA as a third order nonlinear absorption using an elliptical Gaussian beam and 3PA as a fifth order nonlinear absorption using a circular Gaussian beam.<br />In the numerical calculation part some integrals, whose analytically calculation is not possible, have been calculated numerically. Then the numerical calculation results have been compared with analytical calculation results. As the experimental work, open aperture Z-scan technique was employed to determine the 2PA and 3PA coefficients for the prepared samples. Three different type of samples for different purposes have been measured:<br />Two-photon initiators synthesized in the chemistry institute in order to utilize in two-photon induced polymerization, Metal glass composites prepared by ion implantation method and a grafting compound with a commercial name of BAC-M in order to use in photo-grafting process for immobilizing some molecules inside the volume of a polymer matrix.<br />Ultimately, some 3D microstructures were successfully created via both two-photon polymerization and three-photon grafting.