An exciting question in modern magnetism and materials science is whether one can detect, manipulate, and understand collective spins in their highly nonequilibrium, non-thermal states at femtosecond (10-15 s) time scales. Such processes are at least 1,000 times faster than those of the traditional thermal-magnetic processes, which set the upper limit of the magnetic switching time in modern magneto-optical recording technology. First anticipated theoretically in 2006, the first experimental demonstration for light-induced magnetization rotation in the femtosecond regime (âˆ¼200 femtoseconds) in magnetic semiconductors occurred in 2009, using GaMnAs/ GaAs heterostructures of 73 nm thickness. The initial 80-femtosecond laser pulse at 3.1eV induces spin rotation. This rotation angle is measured by a second femtosecond, polarized pulse using the optical Kerr effect (Î¸K). These results provide a strong experimental demonstration of how a laser field can modify the collective spin rotation via photoexcited coherences at femtosecond time scales, much faster than those from thermal fluctuations. In summary, dynamic magneto-optical spectroscopy, exploiting femtosecond laser pulses, was used to demonstrate and explain (via simulations) photo-induced coherent magnetization rotation in a ferromagnetic semiconductor during 100 femtoseconds.