  The transition between the class-B and class-A dynamical behaviors of a
semiconductor laser is directly observed by continuously controlling the
lifetime of the photons in a cavity of sub-millimetric to centimetric length.
It is experimentally and theoretically proved that the transition from a
resonant to an overdamped behavior occurs progressively, without any
discontinuity. In particular, the intermediate regime is found to exhibit
features typical from both the class-A and class-B regimes. The laser intensity
noise is proved to be a powerful probe of the laser dynamical behavior.
