Dynamics of single and two collinearly colliding laser ablated plumes studied using fast imaging and the spectroscopic measurement is reported. The two expanding plumes colliding with each other resulting in the formation of a stagnation layer at the interface region which depend on mean free path and distance between the two plumes. The overlapping region lasts for several microseconds with significant concentration of nanoparticles/ cluster in gaseous phase. The dynamical growth of ZnO nanoparticles is ascertained using Rayleigh scattered second harmonic radiation at 532 nm of Nd:YAG laser. Intensity variation in the Rayleigh scattered signal and blue shift in photoluminescence peak position at different temporal delays with respect to the ablation pulse corroborates the presence and size variation of nano-particles/clusters formed in the vapor phase of ablated ZnO. The thin films of ZnO deposited on glass (polycrystalline) substrate are observed to have preference for single orientation. The presence of low ionic species in the overlap region seems to play a role in getting singly oriented thin films.