Pattern formation and the evolution of complexity in spatially extended dynamical systems has been the subject of many investigations in widely diverse branches of science. In non- linear optics, such studies have been motivated by the goal of developing a general understanding to describe the emergence of periodic and quasiperiodic patterns, vortices or spatial solitons us- ing various nonlinear systems as well as gas, solid-state and semiconductor lasers. These systems are very complex devices having a rich spatiotemporal dynamics. The control parameter that determines the mechanism, which give rise to the transverse structure formation, is the Fresnel number. In this work, we report on numerical and analytical investigations of the wave instability occurring for negative detuning (cavities tuned above resonance) in lasers class B. In that case, relations amongthe decay rate of polarization ,the decay rate of population difference and the cavity rate were γ⊥ À γk À κ. We use the Maxwell-Bloch equations to describe the dynamics of transverse patterns in single longitudinal mode lasers, where the active medium is composed of two level atoms inside a cavity with flat mirrors. An important parameter for determining the behavior of the system is the cavity detuning of field frequency from the atomic resonance transition frequency. With increase of the pump level the homogeneous solution becomes unstable against spatiotem- poral perturbations with a finite wavelength. We have numerically simulated the dynamics of laser field above the second laser threshold in one- and two-dimensional cases. In the result of stability loss of steady solution, the regime that evolves in the system consists of a sequence of switches between traveling wave solutions with different wave numbers. The laser intensity presents the areas of nearly constant values which interrupted by bursts of large amplitude os- cillations. The sequence of wave numbers can be predicted as perturbation with highest growth rate. We use analytical and numerical approaches to perform the linear stability analysis. We found that the regime of dynamical switches is the result of secondary instabilities. By both methods, the evolution may be predicted with a relatively good precision.