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The photochemical reaction of Ge[sup 2+] in 10GeO[sub 2]-90SiO[sub 2] optical fiber preform and the origin of the 5.7 eV optical absorption band induced by intense ultraviolet laser excitation have been investigated using a near-ultraviolet XeF excimer laser (3.7 eV) as the main excitation source. Based on the previous and present experimental results, it is concluded that the 5.7 eV optical absorption band does not originate from the Ge(2) electron trapped center. In place of this model, we have proposed an alternative structural model for the origin of the 5.7 eV band taking into account the experimental fact that the corresponding center is diamagnetic. In addition, it is found that the site selective excitation of the Ge[sup 2+] center can be achieved by using laser sources with different photon energies. [ABSTRACT FROM AUTHOR]

In a 15.7 GeO[sub 2]·84.3 SiO[sub 2] glass prepared by a vapor axial deposition method, optical absorptions at 4.92 and 5.08 eV were observed from 300 to 600 K. The results were then compared with electron spin resonance (ESR) measurement using the same samples. The absorption at 4.92 eV was found to increase with increasing temperature, while the optical absorption at 5.08 eV decreased with increasing temperature. These changes of optical absorption indicate that the concentration of neutral oxygen monovacancy is reduced at higher temperatures. The changes were quite reversible with the temperature. Concentration of Ge E[sup ′] center, estimated from ESR, increased with increasing temperature, which is in contrast with the decrease of neutral oxygen monovacancy. The present result strongly suggests the thermal equilibrium reaction between neutral oxygen monovacancy and Ge E[sup ′] center. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]