Nd:YAG laser induced E' centers probed by in situ absorption   measurements
  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. 
M. Cannas, F. Messina