The response to pump-power modulation of Nd-doped fibre lasers with le
ngths in the kilometre range is reported. The timescales involved are
close to those of subcritical regimes so that the transient relaxation
oscillations are strongly damped. Furthermore, no competing effects (
antiphase dynamics) occur between the two polarization eigenstates of
the laser. Simple rate equations are shown to predict these behaviours
. The experimental side of this study furnishes a definite demonstrati
on of the importance of timescales in the dynamical properties of nonl
inear and nonautonomous physical systems.