Correlation between polarization and intensity in argon-ion lasers

The nature and behavior of the eigenstates of a multimode argon-ion laser containing a variable linear loss anisotropy and submitted to a longitudinal magnetic field are theoretically and experimentally investigated. In particular it is shown that for a given value of the loss anisotropy a transition occurs for a given value of the longitudinal magnetic field. This defines the concept of a critical magnetic field for multimode lasers. For this value of the magnetic field the eigenstates of the multimode laser pass from linearly polarized eigenstates to circularly polarized eigenstates. The shapes of the output spectra for the different behaviors are discussed and observed, and the correlation between the nature of these eigenstates and the output power of the laser is investigated. The puzzling output power enhancement caused by the insertion of a Brewster window is interpreted.