Early Dynamics of a Laser-Induced Underwater Shock Wave

Abstract

The objective of this paper is to observe and investigate the early evolution of the shock wave, induced by a nanosecond pulsed laser in still water. A numerical method is performed to calculate the propagation of the shock wave within 1µs, after optical breakdown, based on the Gilmore model and the Kirkwood-Bethe hypothesis. The input parameters of the numerical method include the laser pulse duration, the size of the plasma and the maximally extended cavitation bubble, which are measured utilizing a high time-resolved shadowgraph system. The calculation results are verified by shock wave observation experiments at the cavitation bubble expansion stage. The relative errors of the radiuses and the velocity of the shock wave front, reach the maximum value of 45% at 5 ns after breakdown and decrease to less than 20% within 20 ns. The high attenuation characteristics of the shock wave after the optical breakdown, are predicted by the numerical method. The quick time and space evolution of the shock wave are carefully analyzed. The normalized shock wave width is found to be independent of the laser energy and duration, and the energy partitions ratio is around 2.0 using the nanosecond pulsed laser.

Comprehensive analysis of spherical bubble oscillations and shock wave emission in laser-induced cavitation

“…1996 a ; Lai et al. 2021). This is because the evaluation of experimental data is based on Hugoniot data valid up to 25 GPa, while the Gilmore model employs the Tait EOS that for very large shock wave velocities yields pressure values that are too low (see § 5.19).…”

“…Furthermore, an ever-larger part of the mechanical energy appears as shock wave energy (Lai et al. 2021). For a 6 ns, 10 mJ pulse with ε = 40 kJ cm −3 , the shock wave energy was found to be more than two times larger than the bubble energy (Vogel et al.…”

“…Experimentally observed pressure decays are usually steeper than predictions by the Gilmore model, with steepest slopes ≥2.0 (Vogel et al 1996a;Lai et al 2021). This is because the evaluation of experimental data is based on Hugoniot data valid up to 25 GPa, while the Gilmore model employs the Tait EOS that for very large shock wave velocities yields pressure values that are too low (see § 5.19).…”

“…With increasing plasma energy density, a smaller fraction of the absorbed laser energy is required for vaporization of the plasma volume and an ever-larger percentage is converted into mechanical energy (Vogel et al 1999b). Furthermore, an ever-larger part of the mechanical energy appears as shock wave energy (Lai et al 2021). For a 6 ns, 10 mJ pulse with ε = 40 kJ cm −3 , the shock wave energy was found to be more than two times larger than the bubble energy (Vogel et al 1999b), different from the case of figure 6 in the present paper, where for ε = 8.7 kJ cm −3 the shock wave energy is slightly smaller than the bubble energy.…”

Near threshold nucleation and growth of cavitation bubbles generated with a picosecond laser

“…The model is adapted to the LIB and phase explosion case by modifying the initial gas pressure to value associated to the laser energy deposited into the plasma and exceeding the steady state condition give in Eq.2. In literature [29] , [30] one can find the calculations of the pressure evolution during laser pulse, but it is for the laser pulse energies (millijoule range) well above threshold and the model is validated for the longer nanosecond pulses, where plasma is strongly absorbing. For picosecond pulses with microjoule energies that were used in our experiments we are close to the bubble nucleation threshold and as such the initial conditions are far from those of highly energetic pulses.…”