ABSTRACT
After several years of rapid development, femtosecond laser pulses entered many labs around the world in the 1980s. It was an exciting time for optical research and beyond. Such a short pulse allows one to investigate events on several hundred down to six femtosecond time scales. This chapter introduces the reader to exciting opportunities at the interface between light and magnetism: How does a laser alter magnetic properties of a magnet on an ultrafast time scale? It focuses on basic concepts and experimental findings in femtomagnetism, while theoretical treatments that require prior knowledge of advanced quantum physics or chemistry are left to the end of the chapter. Time-dependent density functional theory is arguably the most accurate method for femtomagnetism. It is a first-principles method, without any fitting parameters and experimental input, except for the types of atoms and their positions.
