In the initial stage of low fluence ArF laser long term irradiation the absorption behavior in medium-to-high OH containing fused silica materials ([OH] = 250…1400 wt-ppm) depends on the OH content as well as on the initial content of oxygen deficiency centers (ODC). The absorption at a particular fluence (1 mJ/cm2) and its change after 193 nm irradiation (20 Mio. Pulses, 5 mJ/cm2) correlates to the OH content whereas the fluence dependent absorption dk/dH(1…3 mJ/cm2) and its change for the same irradiation conditions follows the initial ODC content. For a more narrow range of the OH content ([OH]  1000 wt-ppm) both, the absorption at a particular fluence and the fluence dependent absorption are correlated to the initial amount of molecular hydrogen in the fused silica.