  Passively mode-locked vertical external-cavity surface-emitting semiconductor
lasers (VECSELs) composed of a gain chip and a semiconductor saturable absorber
have been drawing much attention due to their excellent performance figures. In
this work we investigate how localized structures and incoherent, non-locally
bound, pulse molecules emerge in a long cavity VECSELs using a V-shaped cavity
geometry. We show that these states are bistable with the laser off state and
that they are individually addressable. Using a model based upon delay
differential equations, we demonstrate that pulse clusters result from the
cavity geometry and from the non-local coupling with the gain medium; this
leads to locally independent, yet globally bound phase, incoherent photonic
molecules. Using a multiple time-scale analysis, we derive an amplitude
equation for the field that allows us to predict analytically the distance
between the elements of a cluster.
