Mechanisms of photosensitivity enhancement in OH-flooded standard germanosilicate preform plates

Ge-doped preform plates have been OH-flooded and subsequently exposed to UV pulses from ArF laser (λp = 193 nm) under typical conditions of Bragg grating (BG) inscription. Both Fourier Transform Infrared (FTIR) and Vacuum Ultraviolet (VUV) absorption spectroscopy have been carried out after each step of the sensitization and inscription processes. It is shown that the sensitization process not only induces the formation of a large concentration of hydroxyl species but also that of hydride species and GODC defects. The UV exposure leads to strong changes in both the VUV and FTIR absorption spectra of the sensitized plates. These changes are analyzed with a view to getting a better understanding of the OH-flooding-induced sensitization at 193 nm.