Pattern formation in a laser system: Spontaneous and hard excitation phenomena

We present a study on pattern formation in an optically pumped three-level laser system. In a pump parameter region below the pattern-forming bifurcat ion, the system admits travelling solitary pulse solutions in one-dimension al space and rotating spiral waves in two-dimensional space under hard exci tations. The pattern forming process and geometry are analysed and numerica lly simulated, the two showing a good qualitative agreement. When the contr ol parameters are set beyond the bifurcation point, spontaneous emergence o f spatiotemporal patterns is observed from an initially uniform background, evolving to rolls, dislocations and turbulence through a defect-mediated t urbulence scenario. (C) 1999 Elsevier Science Ltd. All rights reserved.