Practical Studies of Flexible Laser Guiding Systems for Ultra-Violet Laser Transmission

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The interactions between ultraviolet laser and living biotissue were studied. Clean and effective cutting of living soft biotissurs (e.g.muscle, lipid) and hard biotissues (e.g.bone, tooth) has been found without any sign of thermal damage in ArF (wavelength : 193nm) and KrF ( : 248nm) excimer laser irradiation. These excimer lasers will be available to use in the medical fields ; orthopedics, dentistry, opthalmology and cardiovascular surgery. The conventional quartz glass fiber can not transmitted ultraviolet laser under 300nm of wavelength. We have studied the ultra-pure quartz fiber with OH ion doped core for ArF and KrF laser transmission. In this fiber with several hundreds ppm of OH ion, the high transmittance indicated at the initial stage. Therefore, the transmittance was decaying with the repetive pulse transmission. This behavior was caused by E'color center of defect. The transmittance decline was controlled by dopant of the core and clad, by the graded index distribution in clad. E'color center was not a stable defect. This defect was eliminated if the fiber was heated. On the other hand, the fiber with several ppm of OH ion could not be used at the several pulse laser operation. But the transmittance of this fiber increased to 80%/m with the repetive pulse transmission. This increase of the transmittance was caused by the oxygen defect center. This defect was generated in the manufacture process of the fiber, was dissociated by laser transmission. The laser damage threshold of the incident end of the fiber was around 1 J/cm^<2.> pulse. It was so difficult to enhance the delivery energy. The special fiber with conical incident part will be useful for high energy transmission. From the above results, the ultraviolet fiber has many problems. There is every prospect of our solution.