Experimental observation of the effect of pulse duration on optical properties in ultrafast laser micro-processing of polymers

Polymers are important materials for both industrial and scientific applications. However, it is challenging to efficiently process polymers with an ultrafast laser due to their low melting point, high bandgap, and different absorption mechanics with different laser parameters. It is common practice in industries to use different kinds of lasers and, therefore, different laser parameters, such as pulse duration, wavelength, pulse energy, etc. In particular, the effect of pulse duration during ultrafast laser interaction with polymers is significant as the absorption mechanism can be different with different pulse durations. In this study, the effect of pulse duration is investigated during the ultrafast laser interaction with transparent polypropylene (TPP), which is an important polymeric material widely used in many industrial applications. This study is based on the experimental measurement of the optical properties of TPP during ultrafast interaction, where optical properties, i.e., reflectance, transmittance, and absorptance, are determined by performing time-resolved measurements in single-pulse configurations. This experiment is carried out by collecting in situ data of the reflection and transmission of each laser pulse in an ellipsoidal reflector-based experimental setup, which enables the collection of both specular and diffusive reflection with nearly full coverage, and absorption is calculated from the experimental results. It is found that TPP undergoes a dramatic morphological change with different pulse durations ranging from 167 fs to 1 ps, which is correlated with the change of optical properties during the ultrafast laser interaction with TPP for different pulse durations. This result will be useful for controlling the processing of polymers with ultrafast lasers for industrial applications.