New simplified coupling scheme for the delivery of 20 MW Nd : YAG laser pulses by large core optical fibers

The feasibility of transmitting 20 MW, 5 ns laser pulses from a frequency d oubled Nd:YAG laser through a standard 1500 mum multi mode optical fiber is demonstrated. A new coupling scheme employing an optical homogenizer preve nts breakdown in air without the use of a vacuum chamber. At the same time a very homogeneous flat top beam profile on the fiber surface is achieved. The new scheme therefore clearly simplifies fiber coupling of high power la ser pulses. Experiments on the delivery of more than 20000 pulses with 1 10 mJ mean energy without fiber damage have been performed.