  Copper (Cu), gold (Au) (111) crystals were illuminated with 120 fs pulses and
probed by 600 fs X-ray pulses. Rocking curves were measured versus 267 nm (UV)
pump- 0.154 nm probe delay time. Curve width broadening, peak diffracted
intensity and angular shift were recorded for the range of UV excitation
intensities of 2-8 mJ/cm2 . Observed oscillations in time delay dependences of
shift, width and of peak intensity of rocking curves are correlated, as
described by acoustic pulse bouncing between crystal surfaces. In (111) Au,
acoustic pulse originates from pump absorption layer, and peak intensity drops
by a factor of two (at delay time at which sonic wave reaches Au-substrate
boundary) of its initial value prior to absorption of laser pulse. In Cu,
correlated rocking curves dynamics is also observed, however buildup of rocking
curve broadening is faster than one can expect from sonic wavepacket
originating in pump absorption layer. This effect is attributed to acoustic
phonon generation outside of pump absorption layer, it is much stronger in Cu
than in Au. Phonon generation in Cu is distributed throughout the whole bulk of
crystal due to delocalization of mobile hot electrons diffusing from pump
absorption layer.
