Phase Diagrams for CO2 Laser with an Intracavity Saturable Absorber

Abstract

The infrared CO2 laser with an intracavity saturable absorber (LSA) is a system where instabilities in the nonlinear operation may be easily explored. Experimentally the LSA presents a bifurcation between states with time independent laser intensity, i.e. a bistable regime. Furthermore it presents bifurcations to states where the electric field amplitude is modulated in time with a period determined by the relaxation parameters of the laser medium and of the absorber. The modulation should be classified by its amplitude, as large or small. The large amplitude case, where the laser output is composed by pulses with amplitude constant when the bifurcation point is approached, corresponds to the passive Q-switch (PQS) operation, well known from the early development of the CO2lasers. In the small amplitude case the laser output power presents a sinusoidal modulation whose intensity decreases to zero when the bifurcation point is approached.