A theoretical analysis is presented of the active phase mode-locking i
n solid-state lasers when the refractive index frequency dispersion of
intracavity elements is much higher than that of the gain. For such l
aser systems, the steady-state regime of generation of a Gaussian ultr
ashort pulse is found to be unstable due to excitation of other pulses
with Gaussian-Hermitian envelopes. It is shown that this type of inst
ability can be suppressed by placing into the laser resonator an inert
ial saturable absorber with sufficiently small nonlinear losses, which
do not affect energy parameters of the laser emission.