Relationship between laser ablation threshold of graphite-SiO₂ and scattering light signal

As inorganic additional compositions, graphite and SiO₂ have been widely used in ablation coating in the flied of aerospace. Since graphite and SiO₂ have high endothermic enthalpy of reaction under high temperature, graphite-SiO₂ composite has potential applications in the field of high power laser ablation resistance. At present, there are rare reports about laser ablation behavior of graphite-SiO₂, especially the reaction time and ablation threshold. In this paper, the near infrared(NIR) detector was used to detect the scattering light from the irradiated sample surface, and the scattering spectra were processed by differential and fitting method. Based on the scattering signal, the reaction time thresholds of graphite-SiO₂ under different power density were studied combining shape structure analysis of samples after ablation. The result shows that when the sample is irradiated by laser 500 W/cm² for 10 s, there is no mutation abserred in the scattering fitting curve, which indicates that no obvious ablation happened. But when the laser power density increases to 1 000-1 500 W/cm², the apparent turning point in the scattering fitting curve can be observed. The reaction thresholds are 1.5 s and 0.8 s, respectively. By using the laser scattering light signal from the sample surface, the time threshold value of graphite-SiO₂ composite can be effectively characterized.