Simulations of the effects of laser wavelength, pulse duration, and power density on plume pressure generation using a one-dimensional simulation code for laser shock processing

Abstract

We have developed a one-dimensional simulation code for laser shock processing with an atomic model code, an equation of state code, and a laser ablation peening code, in order to calculate laser-plume interactions during laser shock processing. We calculated the temporal changes of some energy ratios [e.g., the ratio (α′) of the thermal energy of a plume to an incident laser energy] and physical quantities, such as electron temperature, ion temperature, absorbed laser power density, and plume pressure under various laser parameters at the laser wavelengths of 355, 532, and 1064 nm. In the case of shorter pulse durations less than 10 ns, a peak plume pressure can be predicted by using α′ of ∼0.25 for 1064 nm and ∼0.40 for 355 and 532 nm below the power density threshold, at which plume pressures start to saturate. These values of α′ were consistent with those obtained in the previous experiments. In the case of longer pulse durations more than 10 ns, α′ for 1064 nm increased up to ∼0.45 at 15 GW/cm2 and an enhanced plume pressure would generate due to plasma absorption via inverse bremsstrahlung absorption in the partially ionized region far from the initial surface of the metal and due to heat conduction of the thermal energy of the plume near the initial surface of the metal. Thus, we showed the validity of our one-dimensional simulation code for laser shock processing and will investigate laser-plume interactions using double pulses during laser shock processing in the future.