The irradiations of vitreous amorphous silica with subband-gap laser radiation at 248 nm induces reversible-irreversible compaction. The former is consistent with the creation of a wide continuum of densified amorphous silica (a-${\mathrm{SiO}}_2$) polymorphs whilst the second stage corresponds to the ablation through laser radiation of the damaged a-${\mathrm{SiO}}_2$. These observations are discussed in terms of conformational structure modifications (i.e., changes in the distribution of planar rings) and stable superficial defect creation.

• Received 26 August 1985

DOI:https://doi.org/10.1103/PhysRevB.33.2972