Optical bistability effects in a dye ring laser

The theory of a homogeneously broadened two-mode ring laser is discussed. Because the mode coupling constant can be twice as great as under conditions of inhomogeneous broadening, new effects like quasi-bistability appear, and the radiation field undergoes a phase transition near threshold that is of the first order. This is reflected in a double peaked probability distribution of each mode intensity, and in alternate switching of the excitation between modes. A first passage time calculation shows that the dwell times should increase rapidly with excitation. These predictions are tested by photoelectric counting and other measurements on a dye ring laser. Although the observed photoelectric counting distributions closely resemble the theoretical ones, measurements of the dwell times reveal significant discrepancies between theory and experiment, that are believed to be due to backscattering. The adequacy of a theory based on two-level atom models in accounting for the behavior of a dye ring laser is briefly discussed.