Shock wave generation in water by nanosecond pulse laser irradiation with 1064 and 2940 nm wavelengths

•Developed a mid-IR rotating mirror Q-switched Er:YAG laser with 350 mJ.•Examined shock wave dynamics generated by focusing the laser on the water surface.•Results with mid-IR Er:YAG and near-IR Nd:YAG laser-induced shock waves compared.•Er:YAG laser can generate shock waves parallel to the beam propagation axis. This study reported a shock wave phenomenon following a laser-induced breakdown in water generated using 1064 nm Nd:YAG and 2940 nm Er:YAG lasers. Previous studies have focused on observing and applying shock waves generated by visible or near-infrared (near-IR) sources and have concluded that these shock waves were directed parallel to the water surface. This study focused on the difference in the directivity of the shock wave in water generated by 1064 and 2940 nm wavelength nanosecond pulsed laser irradiations. We visualized the laser-induced shock waves with high-speed shadowgraphy and numerically measured the pressure with a hydrophone to evaluate the directivity characteristics. The shock wave induced by the near-IR Nd:YAG laser spreads only over a narrow area in a radial direction parallel to the water surface. In contrast, the shock wave induced by the mid-infrared (mid-IR) Er:YAG laser spreads widely in a direction perpendicular to the water surface. This indicates that mid-IR Er:YAG laser can be an underwater shock wave source with the advantages of high photoacoustic conversion efficiency and deep penetration depth, and thus showing the potential to advance diverse applications such as laser surgery and treatment, laser cleaning, laser shock processing, sensing, spectroscopy, and telecommunication.