NONLINEAR TRANSVERSE-MODES OF LARGE-ASPECT-RATIO HOMOGENEOUSLY BROADENED LASERS .1. ANALYSIS AND NUMERICAL-SIMULATION

Transverse pattern evolution is investigated in single-longitudinal-mo de two-level and Raman lasers with flat end reflectors, subjected to u niform transverse pumping. The natural nonlinear modes of the laser ar e identified as spatially homogeneous when the detuning from the gain peak is negative and as ''local'' plane traveling waves when the detun ing is positive. The latter correspond to an off-axis emission of the laser. Stability characteristics of the underlying patterns are predic ted to be quite different for one-dimensional and two-dimensional (2D) lasers. As an illustration, we provide direct numerical evidence for weakly turbulent behavior of a 2D Raman laser where Eckhaus and zigzag phase instabilities act in concert to spontaneously nucleate topologi cal defects and ridgelike illuminated regions. Our numerics also confi rm that the complicated patterns persist for finite transverse pumping as long as the characteristic width of the pump source contains a suf ficient number of selected pattern wavelengths.