  Femtosecond pump probe experiments are reported on quasiparticle relaxation
and recombination in YBa2Cu4O8 as a function of temperature and polarization.
The data show a 2-component relaxation similar to YBa2Cu3O7-\delta, one
component being assocated with the superconducting transition, and the other
with the pseudogap below T* The relaxation time tau_p associated with the
pseudogap is found to be T-independent, while the relaxation time tau_g of the
component obseved only below Tc exhibits a clear divergence near Tc. A strong
polarisation anisotropy of the picosecond transient is observed below Tc which
is attributed to the anisotropy of the probe transition matrix elements.
