Ultrafast Optics IV : Selected Contributions to the 4th International Conference on Ultrafast Optics Vienna Austria This book reflects the most up to date results presented at Ultrafast Optics 2003. The volume contains keynote and invited contributions together with carefully selected regular contributions. The book aims at the highest level of presentation to make it useful as a reference for those working in the field. Ultrafast Optics 1999 and 2001 were published as supplements to Applied Physics B Lasers and Optics