The Optical connectivity (OC) technique introduces a laser beam through an atomiser nozzle and relies on total internal reflection at the liquid interface to propagate inside the continuous liquid to study the instantaneous characteristics of the disintegrating continuous liquid and its interface during the primary atomisation through imaging the emitted fluorescent intensity
from the liquid flow. In the current study, time-dependent OC is used to capture the temporal evolution of the liquid interface structures along the continuous liquid jet injected by a pressure jet atomiser into quiescent air at conditions leading to breakup within the first and second wind induced regime. Optical Flow Velocimetry (OFV) is developed to measure the local velocity of the interfacial structures of the liquid jet. The results show that the liquid interface accelerates downstream of the nozzle exit. The axial and radial mean and standard deviation of the fluctuations of the velocity of the interfacial structures are quantified. The results demonstrate the significance of liquid viscosity and liquid shear on atomisation.