Delivery of over 100MW-class, Nd : YAG laser pulses using hollow fibers

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Application of Q-switched Nd : YAG lasers emitting optical pulse width of 5-10 ns is rapidly expanding its area since the laser equipment has become smaller and cheaper recently. Common silica glass fibers, however, cannot effectively transmit Q-switch pulses with a peak power more than 1 MW because of the damage at the input end and the core induced by radiation of high-energy density pulses and nonlinear effect of silica glass. Therefore, the purpose of our research is to expand the application area of Q-switched Nd : YAG lasers which is currently limited by the above fact. Our final goal is to develop a delivery system based on hollow glass fibers which deliver optical pulses with more than 100 MW of peak power.The following results were obtained in this research :(1) Design and fabrication of polymer-coated hollow fibers by using a liquid-phase fabrication method.To lower scattering losses for visible and near-infrared light, smoothness and uniformity of metal films coated on the inside of hollow fibers are improved. A silver film formed by a conventional mirror plating technique.. It was found that the smoothness and uniformity are greatly improved by keep the reaction temperature at constant by using a newly developed, water cooling system. Fibers fabricated using the new system showed low delivery losses specially for 2nd and 3rd harmonic pulses of Nd : YAG laser light.(2) Development of input couplers and gas-introducing systemTo suppress air-breakdown induced when radiating high-energy optical pulses, a input coupler which introduce inert gas to a hollow core region of fibers was designed and fabricated. This coupler enables delivery of Nd : YAG laser pulses with more than 10 MW of peak power.