Equations of motion for the magnetization in an optically oriented spin system

The spin system is present in conditions of optical orientation and magnetic resonance. The equations of motion are derived for coherent and incoherent excitation. In the latter case (light propagating along the magnetic field) the equations take the form of Bloch's equations and contain the relaxation times ₁ and ₂ as well as the equilibrium z component m_oz, these being dependent on the light intensity. Coherent excitation (circularly polarized light propagating perpendicular to the magnetic field, or two rays perpendicular and parallel to the magnetic field, or two rays perpendicular and parallel to the field) produces equations containing the equilibrium transverse magnetizations produced by optical orientation. In both cases the frequency of the magnetic resonance is shifted by an amount proportional to the light intensity.