Ultra-thin continuous Ni films of 5-25 mn thickness on K8 glass and ZrO2 su
bstrates were investigated by two methods of coherent four-photon picosecon
d (20 ps pulse duration) spectroscopy: the biharmonic pumping technique (BP
) and degenerate four-photon spectroscopy (DFPS), Specific resonant feature
s were found in the self-diffraction efficiency as a function of BP compone
nts' frequency detuning and of pumping wavelength in DFPS, By the model, ta
king into account the real electronic structure of Ni, this structure quant
um-size renormalization and spin splitting, main inter-band and intra-band
relaxation processes, saturation and selection rules for electronic transit
ions, interpretation of the obtained results was performed. It was shown th
at the developed model enables one to explain the results obtained if we as
sume that (i) an electronic subsystem temperature Theta(c) decreases abrupt
ly in a frequency-degenerate case due to efficient direct energy transfer f
rom the electronic subsystem to resonant acoustic phonons and (ii) spin spl
itting of the sample electronic structure is determined by Theta(e). The in
ter-band polarization relaxation time T-2 = 200-250 fs was estimated. Copyr
ight (C) 2000 John Wiley & Sons, Ltd.