Quantum theory of coherent transverse optical magnetism

Density matrix theory is presented to explain recent experimental observations of intense optically induced magnetism due to a “mixed” type of nonlinearity proportional to the product of the electricand magnetic-field strengths of light. Two previously unknown quadratic optical effects are predicted—namely, transverse optical magnetization and magnetic charge separation—and quantitative agreement is obtained with experimental results regarding the former of these. The mechanistic origin of a third quadratic nonlinearity, namely, magneto-electric second-harmonic generation, which is familiar on a phenomenological basis in classical nonlinear optics, is also examined. Transverse optical magnetism is shown to enable large permeability changes at optical frequencies accompanied by magnetic dispersion near resonances. This phenomenon provides for alloptical generation of magnetic moments, large transverse magnetic fields, static electric dipoles, and terahertz radiation in (unbiased) transparent homogeneous dielectrics or semiconductors. Intriguing possibilities for applications are considered, including magneto-electric refractive index modification, optical electric power generation, and spin control. © 2009 Optical Society of America OCIS codes: 190.0190, 190.4410, 190.7110, 320.7120.