A Universal Theoretical Model for Thermal Accumulation in Materials During Repetitive Pulsed Laser Processing
C.H. Li, X. Ju, W.D. Wu, Q.H. Zhu and W.G. Zheng
This work is designed to present a universal theoretical model to study the repetitive pulsed laser-induced thermal integration process in materials. Thermal integration in materials induced by laser pulses has become a very important issue as a result of that pulsed laser heating is widely employed in high-tech industries such as surface processing, thin solid films, laser machining and three-dimensional (3-D) printing in recent years. In these laser-based techniques, knowledge of the temperature distribution in materials is the basis for optimization of process parameters and product quality control. In this work, using the Green function method, the analytical solution formula for temperature field in materials induced by repetitive pulsed laser heating is mathematically deduced based on the Fourier heat transfer theory. In order to get an analytical solution independent of material properties, the obtained temperature field formula is then derived into the dimensionless form. To investigate the effect of two key parameters of laser pulse on thermal integration process, the pulse spacing to pulse width (tc/th) ratio and the laser intensity ratio are carefully examined with the dimensionless analytical solution formula. Results reveal that both tc/th ratio and laser intensity ratio exert direct influence on the thermal integration process. For a setting value of laser intensity ratio, the thermal integration is mainly controlled by the tc/th ratio, and the peak temperature difference drops exponentially as the tc/th ratio (<25) increase linearly. For a given cooling period, the correlation between peak temperature difference and laser intensity ratio is linearly, and there is a specific laser intensity ratio which in turn results in a steady temperature distribution. Furthermore, the analytical formula is applied to study temperature distribution in materials of SiGe thin solid films and fused silica substrates induced by pulsed laser. The analytical formula of temperature field can be beneficial to thermal integration in materials induced by pulsed laser for lots of laser-based technologies.
Keywords: Laser processing, thermal conduction, thermal integration, analytical formula, pulse parameter, Green function