Patterns and solitons in non linear resonators

A laser resonator of large aperture and containing an internal saturable absorber shows bistability and is thus suited to support spatial solitons. If the laser emits in a single longitudinal mode without much detuning, single spatial solitons can be observed which are stationary. They do not move unless driven by noise or in the presence of field - or material gradients. Stronger pumping of the laser results in large numbers of independent spatial solitons. Under the influence of the intensity gradients caused by the optical pumping with a Gaussian-shaped laser beam, the solitons drift away from the optical axis towards the laser emission boundary at which they extinguish. We observe that this continual disappearance of solitons at the boundary is balanced by generation of new solitons in the central area by continual splitting of existing solitons. With the pump on, the laser resonator is initially below threshold, due to the large unsaturated absorption of the BR. The absorption is then completely bleached (at full laser pump) by external laser light, resulting in emission as in the absence of the saturable absorber. The pump was then reduced to partially unsaturate the (BR-) absorber so that its nonlinearity comes into play, and solitons appear.