VUV absorption tail changes of fused silica during ArF laser irradiation

Vacuum UV (VUV) absorption spectra of fused silica were measured during irradiation by 3×106 pulses from an ArF laser (193 nm, 120 mJ/cm2, 200 Hz repetition rate). The absorption increased over the whole spectral range (160–220 nm) and the absorption edge was shifted to longer wavelength upon laser irradiation. The absorption tail of the two irradiated samples flattened as characterised by the Urbach energy increase from initially 146 and 147 to 182 and 190 meV, respectively.