Theoretical simulation of laser-supported absorption wave induced by millisecond-nanosecond combined-pulse laser on silicon

Abstract

In this paper, we established a two-dimensional spatial axisymmetric finite element model to simulate the laser-supported absorption wave (LSAW) induced millisecond-nanosecond (ms-ns) combined-pulse laser (CPL) on silicon, made theoretical investigation. And the finite element analysis software, COMSOL Multiphysics, was utilized in the research. we simulated the propagation procedure of LSAW based on hydrodynamic theory. All the important physical process were considered in the model which were inverse bremsstrahlung, thermal radiation, heat conduction and thermal convection. We simulated silicon irradiated by ms-ns CPL in the case of different pulse delay and ms laser energies, the pulse delay is 1ms, the ns laser energy is 0.1J, the ms laser energy was 3J, 4J, 5J, 6J, respectively. We first obtain the simulation result of velocity fields of LSAW, the results showed that the velocity of LSAW induced by ms-ns CPL decreases with the increasing of ms laser energy. Aiming at obtaining the relationship between the velocity of LSAW, ms laser energies and pulse delay. We keep the ns laser energy density unchanged, the pulse delay was 0, 0.2ms, 0.4ms, 0.6ms, 0.8ms, 1ms, 2ms, 3ms, respectively; the results showed that when the pulse delay is 0.8ms, the ms laser energy is 3J, the velocity of LSAW induced by ms-ns CPL increases obviously. It may be due to the plasma induced by ms laser provides initial electrons for the ns laser ionizing the silicon to produce plasma. The results of the study can be applied in the laser propulsion and laser enhancement technology, etc.