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

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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.