A universal theoretical model for thermal integration in materials during repetitive pulsed laser-based processing

In laser-based techniques such as laser processing, knowledge of the thermal integration process and temperature distribution in materials is the basis for process parameters optimization and product quality control. This work presents a universal theoretical model to study the repetitive pulsed laser-induced thermal integration in materials. Using the Green function method, the analytical solution formula for temperature field induced by laser pulses is mathematically deduced based on the Fourier heat transfer theory. Effects of two key parameters of laser pulses, i.e. the pulse spacing to pulse width ratio (tc/th) and the intensity ratio (I/I0) on thermal integration are studied. Results reveal that for a given I/I0, thermal integration is mainly controlled by the tc/th ratio, and the peak temperature difference induced by adjacent laser pulses drops exponentially as the tc/th ratio (<25) increases linearly. For a given cooling period (tc/th=1), the peak temperature difference induced by adjacent laser pulses changes linearly with the ratio of I/I0. Therefore, temperature distribution in target materials can be tuned by adjusting I/I0 or tc/th of laser pulses. Furthermore, the analytical solution formula is applied to model temperature distribution in SiGe thin solid films and fused silica irradiated by pulsed laser.