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The ablation phenomena in silica glass were investigated using a visible femtosecond laser and time-resolved pump-probe imaging. A pump pulse with a wavelength of 400 nm was employed. Only gentle ablation occurred at a peak fluence of 6.88 J/cm2, and gentle ablation and strong ablation occurred at a peak fluence of 8.23 J/cm2. At both peak fluences, reflectivity increased owing to excitation at a delay time of ~1 ps. At a delay time of ~30 ps, a decrease in reflectivity due to melting was observed only at the local fluence that generated strong ablation. The ablation that occurred after melting was considered to correspond to strong ablation. Similar changes in reflectivity were observed for two values of the local fluence that corresponded to gentle ablation. [ABSTRACT FROM AUTHOR]