| Popis: |
Reductions of UV transmission in silica-based multimode fibers, with low-OH or high-OH synthetic silica core, due to optically active UV defects will be shown using pulsed 355 nm (3rd harmonics) and, for the first time, 213 nm (5th harmonics) Nd-YAG lasers. A new experimental set-up with nearly simultaneous laser damage and spectral analysis is proposed and realized, with the main aim that the laser-induced damage can be measured for wavelengths from 190 up to 1000 nm without movement of the fiber under test. In addition, the damaging UV lasers can be easily changed and aligned. For the two wavelengths, the fibers’ UV transmission is quite different. At 355 nm, the low attenuation level lead to a nearly constant intensity along the fibers, within approx. 10 m. Therefore, the almost constant twophoton absorption is responsible for a homogeneous axial distribution of optically active UV defects, well known below 280 nm wavelengths. At 213 nm, these defects can be generated by one photon alone. However, the defect concentration depends on the axial position and is significantly higher than the wellknown values during D2-lamp irradiation. |
