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

研究了紫外激光与活体生物组织的相互作用。在ArF（波长：193nm）和KrF（波长：248nm）准分子激光照射下，清洁有效地切割活体软生物组织（如肌肉、脂质）和硬生物组织（如骨骼、牙齿），没有任何热损伤的迹象。这些准分子激光器将可用于医疗领域；骨科，牙科，眼科和心血管外科。传统的石英玻璃纤维不能传输波长在300nm以下的紫外激光。研究了掺OH离子的超纯石英光纤在ArF和KrF激光传输中的应用。在该光纤中，OH离子含量达数百ppm，在初始阶段表现出高透光率。因此，透过率随脉冲的重复传输而衰减。这种行为是由E'色心缺陷引起的。透光率的下降受堆芯和包层的掺杂、包层中指数的梯度分布控制。E色心不是一个稳定的缺陷。如果对纤维进行加热，就可以消除这种缺陷。另一方面，含有几ppm OH离子的光纤不能用于多脉冲激光操作。但随着脉冲的重复传输，该光纤的透光率提高到80%/m。透光率的增加是由氧缺陷中心引起的。这种缺陷是在光纤制造过程中产生的，通过激光传输来解离。光纤入射端的激光损伤阈值约为1 J/cm^<2。>的脉搏。提高传递能量是如此困难。具有锥形入射部分的特殊光纤将用于高能传输。从以上结果可以看出，紫外纤维存在许多问题。我们的解决方案大有希望。

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.