Vectorial excess noise factor in common lasers

The fundamental linewidth of usual lasers containing linear phase and loss anisotropies is experimentally and theoretically investigated. It is proved that the eigenstates of such lasers are in general nonorthogonal, leading to the prediction of an important excess noise factor. The experiment evidences an enhancement of the Schawlow-Townes linewidth up to a factor of nearly one hundred, in good agreement with theory.