Colliding micro-shock waves

Shock waves, disturbances that propagate with supersonic velocity in a fluid, are prevalent in nature and across nearly all natural sciences. They find diverse applications in fields such as medicine, aerospace engineering and physical chemistry, where experiments are conducted mostly in macroscopic tubes with an inner diameter ranging from more than 1 mm up to the meter scale. While the theoretical framework for macroscopic shock waves is well-established, the behavior of shock waves in capillaries with diameters in the micrometer range-referred to as "micro-shock waves"-remains largely unexplored. This paper presents novel experimental investigations on the collision of shock waves in micro-capillaries, a fundamental research that has never been done before. These investigations, involving both steady and unsteady drivers, are of significant importance for shock wave physics in general, especially given the limited research on unsteady shock wave collisions. Even more, they play a crucial role in the analysis of micro-shock waves, since they contribute to a more complete characterization of the post-shock region. With the growing interest in microfluidic devices, this research is also important to advance the understanding of supersonic flows at the microscale. Even in the application of high-repetition-rate laser sources, micro-shock wave physics is involved.