The effects of secondary cavitation position on the velocity of a laser-induced microjet extracted using explainable artificial intelligence

Abstract

The control of the velocity of a high-speed laser-induced microjet is crucial in applications such as needle-free injection. Previous studies have indicated that the jet velocity is heavily influenced by the volumes of secondary cavitation bubbles generated through laser absorption. However, there has been a lack of investigation of the relationship between the positions of secondary cavitation bubbles and the jet velocity. In this study, we investigate the effects of secondary cavitation on the jet velocity of laser-induced microjets extracted using explainable artificial intelligence (XAI). An XAI is used to classify the jet velocity from images of secondary cavitation and to extract features from the images through visualization of the classification process. For this purpose, we run 1000 experiments and collect the corresponding images. The XAI model, which is a feedforward neural network (FNN), is trained to classify the jet velocity from the images of secondary cavitation bubbles. After achieving a high classification accuracy, we analyze the classification process of the FNN. The predictions of the FNN, when considering the secondary cavitation positions, show a higher correlation with the jet velocity than the results considering only secondary cavitation volumes. Further investigation suggested that secondary cavitation that occurs closer to the laser focus position has a higher acceleration effect. These results suggest that the velocity of a high-speed microjet is also affected by the secondary cavitation position.