INSTABILITIES IN A BIMODE CO2-LASER WITH A SATURABLE ABSORBER

We report on the observation of mode hopping in a bimode CO2 laser with a saturable absorber. When the control parameters are changed, the output intensity of this laser shows a succession of periodic regimes that may become completely erratic. Each of these regimes may be explained considering the role played alternatively by two unstable fixed points corresponding to the steady state intensity of each mode. In a particular range of the parameter space, a description of multipeaked regimes is given using the Farey arithmetic, and it ressembles that observed in the Belousov-Zhabotinskii reaction. Transverse effects are observed that result from the nonlinear coupling of transverse cavity modes with both the active and passive media. © 1990.