Characteristics of 5‐eV absorption band in sputter deposited GeO2‐SiO2 thin glass films

Thin films (4.6 μm thick) of 5 GeO2‐95 SiO2 and 55 GeO2‐45 SiO2 (mol %) glasses were prepared by rf sputtering method in an Ar‐O2 atmosphere. An intense absorption band at around 5 eV was distinctly observed in both films after the as‐deposited films were annealed at 350 °C for 30 min in a vacuum. A part of this 5‐eV band was gradually decreased by UV irradiation. Saturated absorptivity changes (−Δα∞) of the UV bleached component, which is considered to be the origin of Hill gratings [K. O. Hill, Y. Fujii, and B. S. Kawasaki, Appl. Phys. Lett. 32, 647 (1978)] and second‐harmonic generation in SiO2 glass fibers doped with GeO2, after a prolonged irradiation were 50 cm−1 for 5 GeO2‐95 SiO2 films and 400 cm−1 for 55 GeO2‐45 SiO2 films. These values are greater by one or two orders of magnitude than those (∼2 cm−1) of bulk germanosilicate glasses prepared by the vapor axial deposition method.