Generation of femtosecond electromagnetic pulses at the nanoscale

In a material with large magneto-optical susceptibility, due to the Inverse Faraday Effect, circularly polarized optical pulses induce a pulsed magnetic flux. Alternatively, sufficiently intense optical pulses can induce a pulsed magnetic flux by means of ultrafast demagnetization of a metallic thin film or multilayer with a perpendicular magnetic anisotropy. The time varying magnetic flux may induce a transient electro-motive force and electric current in a conducting loop on the surface of the illuminated material. The latter current induces a transient magnetic field that can be used in various nanomagnetic processes. The magnetic field pulses due to the transient current appear to be too short for use in the magnetic field or spin-current induced precessional switching of magnetization. However, our calculations suggest that the magnetic field could lead to ultrafast switching of a nanomagnet overlaid on the surface of the conductor and demagnetized by the same optical pulse. In the case of photo-magnetic pulses due to the Inverse Faraday Effect, the switching direction could be controlled by the helicity of the optical pulse. We also demonstrate that the proposed device, which we call a Faraday Magneto-Optical Transformer, could be used as a Terahertz emitter.