The recent development of x-ray free electron lasers providing coherent, 
femtosecond-long pulses of high brilliance and variable energy opens new areas 
of scientific research in a variety of disciplines such as physics, chemistry, 
and biology. Pump-probe experimental techniques which observe the temporal 
evolution of systems after optical or x-ray pulse excitation are one of the main 
experimental schemes currently in use for ultrafast studies. The key challenge 
in these experiments is to reliably achieve temporal and spatial overlap of the 
x-ray and optical pulses. Here we present measurements of the x-ray pulse 
induced transient change of optical reflectivity from a variety of materials 
covering the soft x-ray photon energy range from 500eV to 2000eV and outline the 
use of this technique to establish and characterize temporal synchronization of 
the optical-laser and FEL x-ray pulses.