Two years ago, UV-improved (UVI-) fibers were described for the first time. These fibers show significantly reduced UV-absorption around 215 nm during the transmission of UV-light from different UV-sources like deuterium-lamps, excimer-lasers and frequency-doubled tunable dyelasers. This improvement has been realized due to a passivation of the generated UV-defects by gas-doping.Depending on the ambient temperature and the fiber diameter, the lifetime of UV-stability was quite different in these first generation UVI-fibers. This long-term behavior has been studied with different illuminations, temperatures and fiber diameters; there is a good agreement between experimental and theoretical data. Additional modifications have lead to a further improvement in the long-term stability. The predicted lifetime of these UVI2-fibers (<1 50 pm) of the second generation at room temperature is longer than I year. In addition, a short-term behavior was observed using diode-array spectrometer. In this case, the influence of temperature on the transient induced losses is significant and will be described.
Silica based optical fibers are in operation for light-guidance in many applications, with wavelengths ranging from 230 nm to 2.2 .tm. At shorter wavelengths, UV-improved fibers (UVI) can be used, which overcome the significant generation of UV-defects and associated loss in throughput using broadband deuterium-lamps or UV-lasers with fixed wavelengths such as excimer-lasers and quadrupled Nd:YAG lasers. Alternatively, many spectroscopic applications need a tunable and powerful UV-light to carry out remote-measurements, in-situ. In addition, specialized fiber-optics probe may be useful.We will report for the first time on the transmission properties of the UVI-fibers with high-power pulsed lasers with wavelengths in the vicinity of the dominant UV-defect at 215 nm using a frequency-doubled dye-laser, tunable from 206 to 245 nm. Due to the high intensity of this pulsed laser system, especially near the fiber frontface, two-photon absorption plays a major role with decreasing wavelength. Therefore, properties such as starting transmission and UV-induced loss were measured as a function of the wavelength and input pulse energy.The envelope of the wavelength-dependent induced losses is comparable with results taken from tests with low-power broadband deuterium-lamps. However, the temporal behaviour during recovery is quite different.
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