Application Of Nonlinear Programming To Determine Laser-Matter Energy Coupling Coefficient

In the domain of laser-matter interaction, energy coupling coefficient is defined as the ratio of absorbed laser energy to incident laser energy. It is an important parameter to indicate laser irradiation effects. When most of the absorbed laser energy is translated into heat energy, energy coupling coefficient is actually the thermal coupling coefficient. The traditional method to determine thermal coupling coefficient using experimental temperature history of certain surface of the material needs much manual adjustment. In this paper, using the same temperature history, a nonlinear programming model is set up to determine, this time automatically, the thermal coupling coefficient. With this method, the thermal coupling coefficient of 45# steel to 1064nm repetitive frequency laser, which varies with temperature, is determined. At normal temperature (300K), the optimization result is consistent with the result by spectrum scanner. The main work includes:1. Based on experimental temperature history, a nonlinear programming model is set up to determine laser-matter thermal coupling coefficient.2. Using control volume integral method, implicit difference equations are induced for one-dimensional and two-dimensional axial symmetric unsteady-state temperature fields with both convective heat transfer and radiate energy exchange considered. Programs are compiled and tested by analytical examples.3. The relation of thermal coupling coefficient with temperature is analyzed briefly.4. Experiment is carried out to measure the temperature history of the rear surface of 45# steel plate irradiated by 1064nm repetitive frequency laser; using variable-metric successive quadratic programming method (SQP), the optimization is done and the thermal coupling coefficient of 45# steel to 1064nm repetitive frequency laser is obtained, in certain temperature scope.