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Many medical applications have been developed using light sources not only in the visible and near infra-red (NIR) regions, but also in the near ultraviolet (near UV) region of the spectrum. Hard Plastic Clad Silica (HPCS) have found much use in medical applications in general, but generally HPCS fibers are not recommended below 400 nm. Here we will describe HPCS fibers with excellent mechanical reliability and with optical losses of only 1.5 dB/m at 275 nm and less than about 0.2 dB/m at 350 nm. How this combination of properties can benefit diagnostic and surgical applications in the near UV will also be discussed.

A number of the properties of HPCS fibers make them very desirable for medical applications, both for laser surgery and for in-Vivo sensing/endoscopy. High core/clad ratios, low loss, small/large core sizes and broad transmission window are of value for different reasons in each of the application areas. Numerous papers, primarily by Ensign- Bickford and by 3M at earlier SPIE meetings, have presented and discussed how the different properties are important in various medical applications1-10.

However, as with all things, there have also been limitations to previously available products. In laser surgery applications there are two primary limitations. At very high laser powers, the cladding will vaporize, particularly near the fiber ends. This limitation is due to the thermal stability of the proprietary cladding materials, to the planarity of the end face, and to minor misalignment of the laser/fiber interface. The ultimate limiting factor is the first one, as improvements will eventually limited to the material thermal properties. The use of lasers operating at wavelengths below 400 nm, the near uv region, had been hampered by the fact that most hard claddings generally absorb light strongly in this region of the spectrum. Current results will show improvements in recent years, especially the latter problem.