B1. Introduction: what is Spin Photonics ?
Spin-photonics is a challenging research field that aims at using photons for storing and processing the information in magnetic media. Currently, the most efficient methods employed in magnetic recording make use of pulsed magnetic fields that allows writing elementary bits of information. Such approach, combined with an efficient transport of electrons without perturbing their spin states, is the core of an emerging field of science and technology named Spintronics. Alternatively, photons can be used to pattern magnetic media as shown in figure 1 and for studying the fundamental properties of the light interaction with magnetic materials. Using photons for writing and erasing elementary bits of information in magnetic media presents several advantages specific to lasers : the adjustable wavelength, the short pulses available in Ultrafast Optics, the ±h spin momentum of photons carried by circularly polarized light. Indeed these advantages are currently being used. For example the laser wavelength can be tuned to resonantly excite spin states in semiconductors; one can think of extrapolating the actual technology well above the GigaHertz bandwidth using femtosecond laser pulses; linearly or circularly polarized light allows selecting specific optical transitions in semiconductors or inducing all-optical switching in ferrimagnetic materials. Although at the present time Spin-Photonics is an emerging field that is far from outperforming the well established all magnetic technology used for example in the commercially available computer hard drives of a few hundreds Gigabytes rotating at a few thousands rd/minutes. Nevertheless, several promising achievements have been made in the past years.