Optical absorption induced by UV laser radiation in Ge-doped amorphous silica probed by in situ spectroscopy

We studied the optical absorption induced by 4.7eV pulsed laser radiation on Ge-doped a-SiO2 synthe-sized by a sol-gel technique. The absorption spectra in the ultraviolet spectral range were measured during and after the end of irradiation with an in situ technique, evidencing the growth of an absorption signal whose profile is characterized by two main peaks near 4.5eV and 5.7eV and whose shape depends on time. Electron spin resonance measurements performed ex situ a few hours after the end of exposure per-mit to complete the information acquired by optical absorption by detection of the paramagnetic Ge(1) (GeO4)– and Ge-E’ (≡Ge•) centers laser-induced in the samples.