Investigations on fibers for high-average-power Nd:YAG lasers for industrial applications

For industrial applications of high-average power Nd:YAG- lasers the laser power is usually transmitted through all- silica optical fibers. The transmission properties of different types of step index and graded-index fibers are investigated, using a multimode high-power Nd:YAG rod laser with 2000 W output power in CW and Q-switch mode. The fibers are step index and graded-index fibers with 400 and 600 micrometers core diameters, different cladding to core ratios and different types of coating materials. The dependence of the output beam parameters, waist diameter and divergence, and the resulting power transmission are given. The upper limits for the maximum beam parameters and maximum laser powers which can be coupled into fibers per limits for the maximum beam parameters and maximum laser powers which can be coupled into fibers without loss, as well as the dependence of the output beam profiles upon the intensity distribution at the fiber input are briefly discussed. The end faces of polished and cleaved fibers are compared. Different set-ups for coupling several laser beams into one fiber, in order to increase the maximum laser power to be transmitted, are discussed. By these means more than 6kW laser power could be transmitted.