Ayadi, S.2020-10-192020-10-192012-01-01Articale in Journal of fundamental and Applied Sciences Vol. 04 N. 011112-9867http://dspace.univ-eloued.dz/handle/123456789/7149Articale in Journal of fundamental and Applied Sciences Vol. 04 N. 01The simplest model of the laser is that of a single mode system homogenously broadened. The dynamical behavior of this laser is described by three differential equations, called Haken-Lorenz equations[1], similar to the Lorenz model [1] already known to predict deterministic chaos. In previous recent work [5-7] we have proposed a simple harmonic expansion method to obtain a series of harmonics terms that yield analytical solutions to the laser equations. This method allows us to derive an analytical expression of the laser field amplitude when this last undergoes a periodic oscillations around zero mean value. We also obtain an analytical expression of the pulsing frequency.frLaser, instabilities and chaos.Article