Recently, low-energy non-thermal switching based upon optically-induced coherent phonons generated by ultrafast femtosecond optical pulses in interfacial phase-change memory has been reported. While the state-change measured by reflectivity was permanent, the underlying mechanism can only be speculated upon. To understand the collective atomic motion that occurs in response to ultrafast optical pulses and its relationship to phase-change, we have initiated pump-probe studies using an optical pump and ultrafast optical pulses from a free-electron laser. We use diffraction to understand the dynamics changes of the lattice in response to ultrafast optical pulses. Here we report on our initial results of lattice dynamics