Scientists in the University of Nebraska MRSEC are using very short light pulses from a femtosecond laser to perturb magnetic materials and to probe their behavior at times after the perturbation. The light pulses are only about 100 millionth-billionths of a second long.
When the "pump" pulse strikes the sample, it acts like a magnetic hammer to quickly change the direction that the magnetization M points. M then spins around (precesses) very rapidly. The much weaker "probe" pulse comes along a short time later and measures the direction in which M points.
By adjusting the delay time between the pump and probe pulses, we get a detailed picture of how the magnetization precesses with time. These investigations provide information that is useful in such applications as magnetic information storage on hard disk drives.
N. I. Polushkin, S. A. Michalski, L. Yue, R. D. Kirby, Phys. Rev. Lett. 97, 256401 (2006).