Nd:YAG laser induced E′ centers probed by in situ absorption measurements

We investigated various types of commercial silica irradiated with pulsed Nd:YAG laser radiation (4.66 eV), energy density of 40 mJ/cm2 per pulse, with exposure times ranging up to 10 000 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, Type I and II [G. Hetherington, K.H. Jack, M.W. Ramsay, Phys. Chem. Glasses 6 (1965) 6], whereas the 5.8 eV band is not detected in the synthetic materials Type III and IV [G. Hetherington, K.H. Jack, M.W. Ramsay, Phys. Chem. Glasses 6 (1965) 6]. These data indicate that the kinetics of E′ centers is affected by their reaction with diffusing molecular hydrogen H2 made available by dimerization of radiolytic H0.