Combined two-photon optical connectivity and planar laser induced fluorescence for instantaneous characterisation of liquid interface during primary atomisation

•The current study demonstrated a new approach to study the instantaneous structure of the surface of an atomising liquid jet exposed to an air crossflow.•Two-photon fluorescence excitation of a liquid can be achieved using a nanosecond Nd:YAG pulsed laser operating at the infrared wavelength of 1064 nm and this can be applied to both Optical Connectivity and Planar Laser Induced Fluorescence techniques to study primary liquid atomisation.•A combined TPE-PLIF and TPE-OC technique allows the capture of instantaneous cross-sectional geometry of the liquid surface normal to the axis of a liquid jet in a crossflow of air under flow conditions that lead to bag breakup regimes, which is difficult to achieve with other available optical techniques due to the influence of the droplet clouds surrounding the liquid core and relevant optical limitation.•The proposed combined TPE-OC and TPE-PLIF technique over two flow conditions of a liquid jet in an air crossflow quantified the variability of the wave structure on the surface of the liquid jet, including the wavelength of the surface wave. The demonstrated technique can be applied to capture the dynamics of the windward cross-sectional geometry at different planes of the continuous liquid core in an air crossflow at bag breakup regimes.