Heat transfer in ultrafast laser tissue welding

The objective of this research is to develop an appropriate model for simulating the transient heat transfer processes in tissue welding subject to irradiation of ultrashort laser pulses. The ultrafast laser tissue welding process is modeled in three steps. First, there is an immediate local temperature response due to radiation absorption during an ultrashort time period. The transient discrete ordinate method is employed to simulate the ultrashort laser pulse transport in tissue. The temporal radiation field is obtained and the lumped method is used for predicting the local temperature response. After a stable local temperature profile is achieved, the second step starts, in which the hyperbolic heat conduction model is adopted to describe the heat transfer. The thermal wave behavior is observed. It is found that the hyperbolic wave model predicts a higher temperature rise than the classical diffusion model. After about five thermal relaxation times the thermal wave behavior is substantially weakened and the heat diffusion predominates. The heat diffusion equation can accurately describe the heat transfer thereafter.