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.