All-optical characterization of single femtosecond laser-pulse-induced amorphization in silicon

The non-destructive optical imaging method of scanning laser microscopy has been used to evaluate quantitatively the thickness of an amorphous layer induced by a single, spatially Gaussian-shaped 130-fs Ti:sapphire laser pulse on n-doped single-crystalline 〈111〉-silicon wafers for laser fluences between melting and ablation threshold. A parabolic thickness profile exhibiting a maximum value of approximately 60 nm has been found for fluences of 80% of the ablation threshold value by means of scanning laser microscopy in combination with a thin film optical model. This suggests that the melt and the amorphous layer thickness are linearly related to each other.