  We report a study of the photoconductivity (PC) induced in different types of
diamonds (type IIa single crystals and CVD) by femtosecond XUV pulses (high
order harmonics - up to 19th - of a titanium doped laser). We also reprot UPS
spectras obtained with harmonics 13 to 29. Depending on the harmonic's order,
the PC signal first increases (orders 9 to 13) and then decreases. If the
increase is easily interpreted as resulting from a carrier multiplication
process, the further decrease has not yet received an explanation. The UPS
measurements also suggest a strong effect of the plasmon relaxation on the
carrier multiplication process. Finally, we performed a preliminary GW
ab-initio calculation of the carriers lifetime, acounting for electron-electron
interactions. In the near-bandgap region, it behaves approximatively according
to the Fermi-liquid model, from which it strongly departs at higher energies,
which is attributed to band-structure effects and to plasmon excitations.
