Heat accumulation effect during CO2 laser processing of fused silica optics

•The heat accumulation effects during fused silica processing under different laser parameters are explored and verified by the three-dimensional numerical simulations and experiments.•Periodic ripple structures on the processed surface are formed by the superposition of laser spot energy.•The fictive temperature of the substrate tends to stabilize starting from the third pulse of each track’s laser scanning.•The thickness of the heat-affected zone is close to the material removal depth, and it can be suppressed by reducing laser pulse width.