  The detection of ultrashort laser-generated acoustic pulses at a metal
surface and the reconstruction of the acoustic strain profile are investigated.
A 2 ps-long acoustic pulse generated in an SrRuO$_{3}$ layer propagates through
an adjacent gold layer and is detected at its surface by a reflected probe
pulse. We show that the intricate shape of the transient reflectivity waveform
and the ability to resolve acoustic pulses shorter than the optical skin depth
are controlled by a single parameter, which is determined by the ratio of the
real and imaginary parts of the photoelastic constant of the material. We also
demonstrate a Fourier transform-based algorithm that can be used to extract
acoustic strain profiles from transient reflectivity measurements.
