  All-optical switching of the magnetization in magnetic nanostructures by
femtosecond circularly polarized laser pulses has been demonstrated in several
systems. We present a Landau-Lifshitz-Lambda (LLL) model which describes the
magnetization dynamics using three density states: two ferromagnetic grounds
states and an excited optical state. One of the ferromagnetic ground states is
optically excited by circularly polarized light to a spin reversed state, which
is then "Coulomb collapsed" to the magnetization reversed ground state. The
time evolution of the optically excited states is described by a Lindblad
master equation, in which the optical excitation is introduced via the
Hamiltonian. Dissipation terms are introduced via Lindblad operators. The LLL
model combines the precessional motion of the magnetization described by the
Landau-Lifshitz theory, with the response of the three level Lambda system. The
optical excitation lasts for the duration of the laser pulse and the system
relaxes at a fast rate due to the electron-electron interaction. We study the
solution of the eigenvalues problem of the optical equation of motion for the
magnetization and identify a coherent and incoherent regimes and derive an LLL
model that can be integrated with existing micromagnetic codes to describe
optical excitation of magnetic materials.
