Photoinduced changes in UV absorption spectra of nitrogen-doped silica caused by exposure to ArF excimer laser

Absorption spectra of high-purity silica, in which 1.2% or 3.0% oxygen atoms are replaced by nitrogen, are measured in the spectral interval of 3.0-6.5 eV. Photoinduced changes of these spectra when exposed to 193 nm wavelength excimer laser radiation, pulse intensity being ∼50 mJ/cm2, are examined. Absorption spectra relaxation under subsequent annealing as well as changes brought about by saturation of glass with molecular hydrogen are studied. Parts of graded-index fiber ∼1 mm in length and 200 μm thick transverse slices of a fiber preform served as samples. It is found that exposure of fiber samples to laser irradiation brings about a significant decrease of initially more intense absorption band of Si-ODC in the region of 5.0 eV and an increase of initially less intense band centered at 5.8 eV at a time. In bulk samples correlation of these bands is opposite, photoinduced changes are less expressed against structureless absorption tail increase in the spectral interval of 3.0-6.5 eV. It is shown that subsequent 20 min 700 °С annealing leads to the relaxation of photoinduced changes in absorption spectra in bulk and fiber samples. By placing irradiated samples into molecular hydrogen atmosphere at room temperature absorption bands are suppressed and transparency at shorter wavelengths of UV region is increased. Data obtained is discussed in the context of photosensitivity of nitrogen-doped silica-core fibers, which serve a technological platform for thermoresistant in-fiber Bragg gratings fabrication.