Ultra-Low Loss Hollow Waveguides for 5-kW Class Laser Light

为了实现高功率激光在红外波段的传输，我们研究了一种介质涂覆的空芯波导。降低波导损耗和改善输出光束质量是我们的主要目的。今年的研究结果如下。(1)CO本文采用ZnS作为介质涂层波导的涂层材料。ZnS具有低折射率、高耐久性和无毒的优点。制作的ZnS涂层波导对CO_2激光的损耗为0.25dB/m（1 mm口径波导）。此外，它表明，ZnS涂覆的银波导的耐久性是优异的。我们还测试了CO和Er：YAG激光器的性能。结果，波导对于两种激光器都具有良好的特性。特别是在Er：YAG激光器中，该波导能够承受800 mJ的脉冲能量和10 pps的重复频率的高功率激光输出。（2）用于制造波导的心轴的改进希望在波导的制造过程中使用的心轴在其形状或表面上没有不规则性。我们新使用的铝管涂有聚酰亚胺薄膜作为心轴，以满足条件。使用新芯轴制作的波导显示出更低的损耗和更好的光束质量。此外，我们正在研究玻璃心轴管作为一种理想的。

To realize delivery of high-power laser light in an infrared region,we have studied a dielectric-coated hollow waveguide. Loss reduction of the waveguide as well as improvement of output-beam quality is our main purpose. The result of this year's research is as follows. (1)CO_2,CO,and Er:YAG laser delivery by ZnS-coated Ag waveguidesWe have newly adopted ZnS as a coating material for the dielectric-coated waveguide. ZnS has advantages that are the low refractive index,high durability,and non-toxicity. Fabricated ZnS-coated waveguide showed the low-loss,which is 0.25 dB/m(1 mm-bore waveguide) for the CO_2 laser light. Furthermore,it was shown that the durability of the ZnS-coated Ag waveguide is excellent. We also examined the performance for CO and Er:YAG laser. As a result,the waveguide has a good property for the both lasers. Especially for the Er:YAG laser,the waveguide endured delivering the high laser power, the pulse energy of 800 mJ and the repetition rate of 10 pps. (2)Improvement of the mandrel for fabrication of the waveguideIt is desirable that the mandrel used in the fabrication process of the waveguide has no irregularity in its shape or surface. We have newly used the Al tube coated with a polyimide film as a mandrel to satisfy the condition. The waveguide fabricated using the new mandrel showed a lower-loss and a better beam quality. Furthermore,we are investigation the glass mandrel tube as an ideal one.