THEORETICAL MODELING AND TRANS-SCALE SIMULATION OF COUPLING FIELDS GENERATED BY THE EXPLOSION OF A FOCUSED HIGH POWER LASER BEAM

The study of coupledelectromagnetic and thermo-mechanical processes concerning with afocused high power laser explosion in gas medium is now becomingan important research forefront. The subject includes a series ofenergy absorption and transfer processes, such as ionization andoptical breakdown in mixture gases, the evolution and propagationof the laser supported combustion wave (LSC) and laser supporteddetonation wave (LSD) in gas-plasma.In fact, these very complex processes can be macroscopicallyconsidered as interactions between three distinct phenomena, thatis, laser scattering, high temperature as well as high speed flowin gas plasma. In the present paper, we are mainly concerned withthe coupling effects between the electromagnetic wave propagationand the thermo-mechanical flow field, that is, the couplingbetween Maxwell equations which describe the electromagnetic waveinduced by laser, Navier-Stokes or Euler equations of gasdynamics, thermodynamic Equation of State, the Saha equation ofionization balance (Saha Eq.), the evolution and propagation ofLSC/LSD waves and the recoil pressure and impulse.This research works cover three stages. In the first one, thelaser scattering in inhomogeneous mixture and laser wavepropagation is modeled based on the Maxwell-Euler equations.In the second, a numerical model for ignition and/or opticalbreakdown of combustible mixture gases under the radiation of highpower laser is presented. The electromagnetic fields of laser beampropagating through mixtures are simulated by directly solvingMaxwell equations with FDTD scheme and free-reflection boundaryconditions. The fine structures of the power density distributionnear the focus center are revealed by means of coupling numericalanalysis of Euler equation and EOS for heat diffusion andconvection, Saha equations of ionized gas in equilibrium state anddetailed chemistry mechanism. Because the dielectric propertiesare changed with thermal state of the gas mixtures during theradiation, therefore, a unified scheme are developed by combiningCIP scheme for LSC/LSD propagation with FDTD solver for Maxwellequations over the uniform grid cells. The finer structures ofpower flux near the focus have been revealed and visualized fromnumerical results, depending on the power level and incidentangles of the laser beam.In the third stage which is now underway, models and simulationtechnique will be developed and extended to more complicated flowprocesses.