Controlling spins with light.

The interaction of sub-picosecond laser pulses with magnetically ordered materials has developed into an extremely exciting research topic in modern magnetism. From the discovery of sub-picosecond demagnetization over a decade ago to the recent demonstration of magnetization reversal by a single 40 fs laser pulse, the manipulation of spins by ultrashort laser pulses has become a fundamentally challenging topic with a potentially high impact for future spintronics, data storage and manipulation, and quantum computation. We have recently demonstrated that one can generate ultrashort and very strong (teslas) magnetic field pulses via the so-called inverse Faraday effect. Such optically induced magnetic field pulses provide unprecedented means for the generation, manipulation and coherent control of spins on very short time scales. The basic ideas behind these so-called opto-magnetic effects will be discussed and illustrated with recent results, demonstrating the various possibilities of this new field of femto-magnetism.