Absorption and temperature distribution during ultrafast laser microcutting of polymeric materials

Abstract

Material processing by ultrafast lasers is an attractive technology for high-precision fabrication, such as cutting, drilling, and surface modification, of a wide range of material, including dielectrics, semiconductor, metals, and polymer composites. However, it is still challenging to apply ultrafast laser processing in many applications because some key processes, such as absorption and heat accumulation, are not fully understood, especially for polymeric materials, which have a low melting temperature and, therefore, are more vulnerable to thermal damage. In this study, an analytical solution to a transient, two-dimensional thermal model is derived using Duhamel's theorem and Hankel’s transform method to understand the effect of laser parameters during ultrafast laser interactions with polypropylene (PP), which is a material widely used in many industrial applications. To correlate with theoretical calculation, laser cutting experiments are carried out on PP sheets. This study found that the total energy absorbed in the material and the laser intensity are two important factors to estimate the laser processing performance. In addition, time-resolved measurements are performed by using fast photodiodes and an oscilloscope to understand the dynamics of ultrafast laser interactions during the laser cutting process. Transmitted and reflected signals are monitored and analyzed to extract information on nonlinearity and the absorption coefficient.