Shock wave trains in liquid jets were previously generated only by ablation with femtosecond x-ray lasers. Here we show that shock trains in water microjets can be also generated using nanosecond green laser pulses with 1- to 10-mJ energy. The ablation of 15-, 20-, 30-, and 70-$\mu \mathrm{m}$ water microjets opened a gap in the jets and launched an initial shock wave. Fully developed shock trains were observed in the 30- and 70-$\mu \mathrm{m}$ jets up to 250-ns delays, and these trains were also transmitted inside the nozzles. A few tens of nanoseconds after the pulse, the shock dynamics and its pressure became similar to the ones generated by x-ray lasers, with a more rapid pressure decay in thinner jets. At time delays exceeding 100 ns in the 30-$\mu \mathrm{m}$ jets, the leading shock pressure stabilized to an approximately constant pressure of 40 MPa. The energy density deposited in the jets was estimated at 30 MJ/${\mathrm{cm}}^3$ by comparing the jet gaps in the green and x-ray laser experiments, and matched previous estimates for optical ablation in water. The pressure decay in the 30-$\mu \mathrm{m}$ jets was modeled based on the pressure decay observed in x-ray laser experiments.

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• Lasers
• Shock waves
• Laser ablation