Interaction of vacuum ultraviolet excimer laser radiation with fused silica: II. Neutral atom and molecule emission

We report mass-resolved time-of-flight measurements of neutral Si, O, and SiO from ultraviolet-grade fused silica during pulsed 157-nm irradiation at fluences well below the threshold for optical breakdown. Although the emission intensities are strongly affected by thermal treatments that affect the density of strained bonds in the lattice, they are not consistently affected by mechanical treatments that alter the density of point defects, such as polishing and abrasion. We propose that the absorption of single 157 nm photons cleave strained bonds to produce defects that subsequently diffuse to the surface. There they react with dangling bonds to release neutral atoms and molecules. Hartree-Fock calculations on clusters containing these defects support the contention that defect interactions can yield emission. More direct emission by the photoelectronic excitation of antibonding chemical states is also supported.