Ultrafast Electron DiffractionStudies of Optically ExcitedThin Bismuth FilmsVom Fachbereich Physik der Universitat¨ Duisburg Essen zurErlangung des akademischen Grades eines Doktors derNaturwissenschaften genehmigteDissertationvonIvan RajkovicausAleksinacReferent: Prof. Dr. Dietrich von der LindeKorreferent: Prof. Dr. Michael Horn von HoegenTag der mundlichen¨ Prufung:¨ 21.10.2008AcknowledgementsI would like to thank my supervisor, Prof. Dr. Dietrich von der Linde, forproviding me with the opportunity to do my PhD thesis research in his group atthe Institut fur¨ Experimentelle Physik at the University of Duisburg Essen andfor his support and guidance during my work there.I would also like to give special thanks to the people I worked with on thisproject, Ping Zhou and Manuel Ligges. Without them, this work would not bepossible.Then, I would like to thank Nikola Stojanovic´ for all of his help, both in andout of the lab.Many thanks go to all of the people working in the AG von der Linde:Dr. Klaus Sokolowski Tinten, Dr. Alexander Tarasevitch, Matthieu Nicoul, Dr.Uladzimir Shymanovich, Stephan Kahle,¨ Dr. Oliver Heinz, Dr. Vasily Tem nov, Wei Lu, Jan Gohre,¨ Konstantin Lobov, Barbel Maullu,¨ Dr. Ulrich Teubnerand all of the diploma students and the student assistants who contributed to thewonderful working atmosphere in this group.A special thanks to Mrs.