The stability of passively modelocked lasers with fast saturable absor
bers is investigated using the aberrationless approximation of soliton
theory. A new analytical criterion for the stability of soliton solut
ions in a system with weak absorber saturation is presented. If the ga
in-saturation energy is arbitrarily large, asymptotically stable solut
ions require strong absorber saturation. (C) 1997 Elsevier Science B.V
.