Antiphase dynamics in an optically pumped bidirectional ring laser

We present experimental evidence of antiphase dynamics in an optically pumped NH3 bidirectional ring laser. We show that under strong mode-mode coupling between the forward and backward modes of the laser, the steady output in both directions of the laser becomes dynamically unstable. Depending on the mode interaction strength, the intensity evolution of each mode can be periodic or chaotic. Under certain conditions a period-doubling route to chaos was observed. However, no matter what state the laser is, even under the influence of another instability, the intensity variations of the two modes caused by the mode interaction are always antiphase, showing that they are in a collective self-organized state.