Ultrasound emission monitoring Drilling of micro cooling holes on turbine components is of critical importance for the performance of a jet engine. Water jet guided laser is a convenient processing method to drill such holes. When laser and water jet are used together, the machining region is simultaneously cleaned and cooled increasing the overall quality. It is also possible to obtain high aspect ratio holes due to the thin water jet guiding the laser for deeper holes. There are many factors in the process affecting the machining efficiency. More research and experimenting are required to understand the effects of the variables on the drilling performance. Especially, material removal differs for various geometries. In this study, experiments are conducted with different hole diameter values to explore the process limits and find out the machining efficiency depending on the hole depth. Additionally, a real-time measurement method based on acoustic signals is proposed. The experiments show a correlation between ultrasound emission and material removal depending on the hole geometry in a water jet guided laser machine.