Study on the ultraviolet nanosecond laser ablation and heat-affected zone of polydimethylsiloxane films based on comprehensive surface analysis

Laser processing of polydimethylsiloxane (PDMS) plays a vital role in many applications. However, questions regarding the PDMS laser ablation mechanism still prevail. Moreover, heat-affected zone (HAZ), a critical issue in investigating and evaluating PDMS laser ablation, has been rarely studied. Here, with surface analysis techniques, such as Raman spectroscopy, atomic force microscopy (AFM), micro-infrared spectroscopy (micro-IR), the ultraviolet nanosecond (UV-ns, 355 nm) laser ablation and HAZ of PDMS films were investigated. Due to the poor absorption of PDMS and the insufficient laser photon energy, the UV-ns laser ablation of PDMS was primarily a photothermal process. The chemical composition of the PDMS film surface changed due to the incomplete decomposition of PDMS and the deposition of decomposition products, leading to Young's modulus of the PDMS film surface increasing from 3.81 MPa to 9.70 MPa. Micro-cracks and micro-wrinkles emerged on the PDMS film surface due to laser-induced thermal stress. For the multi-pulse UV-ns laser ablation of PDMS, the ablation threshold fluence decreased rapidly from 7.15 J/cm2 to 1.46 J/cm2 as the number of pulses increased from 5 to 100 due to the incubation effect. Moreover, the laser-induced photothermal effects resulted in the formation of HAZ, where the chemical composition changed. Laser-affected zone (LAZ) was proposed to investigate the relationships between HAZ and laser single-pulse energy and the number of laser pulses. With the above surface analysis, an effective method of studying the PDMS laser ablation and evaluating HAZ was developed.