Synchronization through bursting oscillations for two coupled lasers

Two CO₂ lasers admitting quite different relaxation oscillation frequencies are coupled through a common saturable absorber. Despite their difference, these two lasers may successfully synchronize by exhibiting different oscillatory behaviors. The response of the low-frequency laser (L₁) consists of strongly pulsating intensity oscillations while the large frequency laser (L₂) exhibits bursting and nearly harmonic oscillations. These bursting oscillations are studied experimentally and numerically in terms of the pump parameter of L₂. Above a critical point, the bursting oscillations are slowly decaying between successive pulses of L₁ but periodic synchronization between lasers remains possible. Below this critical point, the bursting oscillations are slowly expanding between pulses of L₁ and synchronization is no more periodic. These two distinct responses suggest a bifurcation phenomenon that we study analytically and numerically using a continuation method.