  We study the response of the one-dimensional charge density wave in K0.3MoO3
to different types of excitation with femtosecond optical pulses. We compare
the response to direct excitation of the lattice at mid-infrared frequencies
with that to the injection of quasi-particles across the low-energy charge
density wave gap and to charge transfer excitations in the near infrared. For
all three cases, we observe a fluence threshold above which the amplitude-mode
oscillation frequency is softened and the mode becomes increasingly damped. We
show that all the data can be collapsed onto a universal curve in which the
melting of the charge density wave occurs abruptly at a critical lattice
excursion. These data highlight the existence of a universal stability limit
for a charge density wave, reminiscent of the empirical Lindemann criterion for
the stability of a crystal lattice.
