  We investigated various types of commercial silica irradiated with a pulsed
Nd:YAG laser radiation (4.66 eV), with exposure time ranging up to 10000 s.
Transient E' centers were probed in situ by measuring the amplitude of the
optical absorption band at 5.8 eV (due to E' centers) both during and after
irradiation. The laser-induced absorption is observed only in natural samples,
whereas the synthetic materials exhibit high toughness to radiation effect. The
reported results evidence that the kinetics of E' centers is influenced by
their reaction with diffusing molecular hydrogen H2 made available by
dimerization of radiolytic H0.
