Experimental probe into the femtosecond laser ablation thresholds in carbon fiber reinforced polymer and assessment of the measurement theories

Focusing on the femtosecond laser processing of carbon fiber reinforced polymer (CFRP), the ablation threshold is of great concern to fulfill the manufacturing of specified functional surfaces and devices. The ablation thresholds and incubation coefficients of resin matrix and carbon fiber in CFRP subject to femtosecond laser irradiation are investigated from the measurement theories of ablation area diameter and ablation rate. The ablation thresholds of resin matrix and carbon fiber at different laser line scanning speeds are quantitatively determined by the ablation area diameter. Moreover, the impacts of laser scanning speeds, laser scanning directions, and polarization types on the ablation thresholds and incubation effect of resin matrix and carbon fiber in CFRP are revealed in depth, which indicates the ablation thresholds depend on the condition of femtosecond laser processing. In other words, choosing the appropriate combination of laser scanning and polarization would achieve the goal of efficient removal of resin matrix and carbon fiber in CFRP. After assessment of the measurement theories, it is found the one from ablation area diameter is more accurate than that from ablation rate, which is because of the difficulty in correctly measuring the ablation depth with ripples formed on the laser ablated surface.