Prolonged UV radiation, below 260 nm, solarizes untreated fibers, reducing their UV transmittance significantly. Our Solarization Resistant Fibers are protected from the damaging effects of deep UV. Their useful life depends upon three conditions:
1. The wavelength(s) to which the fiber is being exposed (the shorter the wavelength(s), the shorter the lifetime).
2. The intensity of the source (the greater the intensity, the shorter the lifetime).
3. The duration or cycle time (after 1500 hours of exposure to a deuterium source, our 200 µm, 1 m long fiber transmitted ~30-40% of its original throughput at 214 nm).
Fig. 1 The effect of UV exposure on fused silica and solarization resistant fibers.
Fig. 2 Relative transmittance vs time of a 2 m length of Solarization Resistant Fiber.
What Causes Solarization?
Solarization occurs at wavelengths below 260 nm. The effect is created by high-energy UV photons that lead to the generation of defects. These defects cause significant transmittance losses at the shorter wavelengths. The fiber becomes unusable at wavelengths below 260 nm. This effect can be reduced, for a period of time, by infusing hydrogen into the fiber's silica core at very high temperatures. In use, the hydrogen will gradually diffuse out and the fibers will solarize.
Before using, the fiber should be exposed to the UV source for 5 minutes, to allow initial degradation and formation of the Si-H bonds. After this time, equilibrium is reached and you can use the fiber normally. To prolong its life, store the fiber in a freezer, when not in use.
