Terahertz-Magnetic-Field Induced Ultrafast Faraday Rotation of Molecular Liquids.

Rotation of the plane of the polarization of light in the presence of a magnetic field, known as the Faraday rotation, is a consequence of the electromagnetic nature of light and has been utilized in many optical devices. Current efforts aim to realize the ultrafast Faraday rotation on a subpicosecond timescale. Thereby, the Faraday medium should allow an ultrafast process by which in the presence of an ultrashort intense magnetic field, the light polarization rotates. We meet these criteria by applying an intense single cycle THz magnetic field to simple molecular liquids and demonstrate the rotation of the plane of polarization of an optical pulse traversing the liquids on a subpicosecond timescale. The effect is attributed to the deflection of an optically induced instantaneous electric polarization under the influence the THz magnetic field. The resolved Faraday rotation scales linearly with the THz magnetic field and quadratically with the molecular polarizability.