Laser-generated Shock Waves Research Articles

Shock wave decay and spall strength in laser-matter interaction

A new experimental method was developed in order to estimate the decay of the laser-generated shock waves and the dynamic spall pressure. Experiments were performed on aluminum, copper, and unidirectional carbon fiber epoxy composites with impact strain rates of the order of 107 s−1. The following values for dynamic spall pressure and pressure gradient were obtained (to an accuracy of a factor of two): aluminum [25 kb (kb=kilobars), 60 kb/mm]; copper (20 kb, 180 kb/mm); carbon fiber epoxy composite (0.3 kb, 15 kb/mm) perpendicular to the fiber direction; and (7 kb, 100 kb/mm) when the impact is parallel to the fiber direction.

Laser-induced spall in metals: Experiment and simulation

Spall at ultra high strain rate (107 s−1) was investigated using short pulsed laser-induced shock waves in copper and aluminum foils. The intensities of the 3.9-ns Nd:Glass laser were in the range of 1010–1012 W/cm2, and the foil thickness was in the 100–600 μm range. The laser-generated shock wave pressure was in the range of a few hundred kilobars (kb). The shock wave traversed the foils in a few tens of nanoseconds. The controlled stepwise increase in laser energies allowed the stages of damage evolution from incipient to complete perforation of the target foils to be found. The energy threshold for spall and the spall width at that energy was measured as a function of the foil thickness for both materials. At threshold energy conditions, spall width of 25–65 μm for Al and 15–45 μm for Cu were obtained for foil thicknesses of 100–600 μm. Computer simulations of the laser-induced spall were performed, including the laser absorption, shock wave travel through the foil, and the spall phenomena. The simulations were based on the one-dimensional medusa code, which was expanded to include the spall phenomena, using simple spall criteria. An estimate of the strain rate was derived from the simulations and it was shown that the strain rates in the present experiments are about an order of magnitude larger than those obtained in spall experiments using other methods. The experimental results of energy threshold for spall and spall width at this energy were compared with the numerical simulations. The experimental results are in good agreement with the simulation results, indicating that spall strength for both materials, Al and Cu, are in the −50 to −60 kb regime.

Radiation heating in laser-irradiated planar targets

Planar targets of different Z were irradiated with 0.53 μm laser light at intensities ≤5×1013 W/cm2. The target rear surface was observed to be first heated by the laser-generated shock wave. This was followed by a strong second heating which was attributed to radiation transport through the decompressed target. This additional heating might also be responsible for enhancing early laser transmission through thick targets.

Hugoniot measurements for laser-generated shock waves in aluminum.

We report on the first experimental measurement of principal Hugoniots in aluminum for shock pressures of 0.3-12 Mbar generated by laser-driven ablation. These were derived from independent measurements of the shock speed, shock pressure, and shock-heated target temperature. The results showed excellent agreement with LASNEX simulations and with calculations using SESAME equation-of-state data. More importantly, the results indicated that the shock speed and temperature Hugoniot may provide useful equation-of-state studies in laser-generated shock-wave experiments.

An analytical model for creation and decay of strong shock waves caused by a trapezoidal laser pulse

An analytic hydrodynamic model for the formation and decay of strong shock waves (0.1–10 TPa) is derived in this paper by using self-consistent and well-defined assumptions. A trapezoidal pressure profile as a function of time applied to the target surface is used as the initial condition. This model permits the calculation of the pressure, velocity, and acceleration of the shock front, as well as the calculation of the pressure gradient immediately behind the shock front, as functions of time and position. This model is applied to laser-generated shock waves with maximum intensities of 5×1013 and 5×1014 W/cm2. Good agreement with previous computer simulations of solid–laser interaction is obtained.

Formation and decay of laser-generated shock waves

The process of formation and decay of laser-generated shock waves is described by a hydrodynamic model. Measurements of shock velocities are performed on copper foils for incident intensities between 3\ifmmode\times\else\texttimes\fi{}${10}^{11}$ and 3\ifmmode\times\else\texttimes\fi{}${10}^{12}$ W/${\mathrm{cm}}^{2}$, with the use of piezoelectric detectors. Maximum induced pressures are found between 0.5 and 1.2 Mbar in the intensity range considered. Analysis of the results with the shock-evolution model outlines the importance of the decay process of laser-generated shocks.

Laser-generated shock wave experiments at pressures above 1 TPa

Laser-generated shock wave experiments at pressures above 1 TPa

Laser-generated thermoelastic shock wave in liquids

In the present investigation the procedure of matched asymptotic expansion has been applied to obtain a higher approximation for the flow of an incompressible second-order fluid past a porous sphere. The boundary conditions have been satisfied by matching Stokes (inner) and Oseen (outer) solutions of the stream function. The terms in the inner expansion are the solutions of nonlinear partial differential equations which have been solved approximately by expanding in terms of a non-Newtonian parameter S, which is small. The drag experienced by the sphere has been obtained and is discussed for a few particular cases.