  Time-resolved optical experiments can give unique information on the
characteristic length scales of dynamic charge inhomogeneity on femtosecond
timescales. From data on the effective quasiparticle relaxation time &#61556;r
in La2-xSrxCuO4 and Nd2-xCexCuO4 we derive the temperature- and doping-
dependence of the intrinsic phonon escape length le, which, under certain
circumstances, can be shown to be a direct measure of charge inhomogeneity.
Remarkably, a common feature of both p and n-type cuprates - which has
important consequences for superconductivity - is that as T &#61614; Tc from
above, the escape length approaches the zero-temperature superconducting
coherence length, le &#61614; &#61560;s(0). In close vicinity of Tc, le appears
to follow the critical behaviour of the Ginsburg-Landau coherence length,
&#61560;GL(T). In the normal state le is found to be in excellent agreement
with the mean free path lm obtained from the resistivity data. The data on le
also agree well with the data on structural coherence lengths ls obtained from
neutron scattering experiments, implying the existence of complex intrinsic
textures on different length scales which may have a profound effect on the
functional properties of these materials.
