Fibre optic beam delivery of nano-second Nd:YAG laser pulses for micro-machining Available to Purchase

High peak power Nd:YAG laser pulses of nano-second duration are important for a number of laser materials processing applications, including marking and micro-machining. Nd:YAG laser radiation can be transmitted to the workpiece through flexible optical fibres, but the very high peak powers associated with these short laser pulses result in damage problems. Indeed, this damage can occur at significantly lower intensities than with conventional optic components, i.e. bulk materials. Consequently, fibre beam delivery has not generally been used for material processing applications of Q-switched pulses.. We investigated the dependence of damage threshold on fibre input face preparation techniques and improvements in damage resistance by selective conditioning of the laser beam. In particular, we have shown that by using diffractive optical elements (DOE’s) in the fibre coupling optics, a substantial improvement in damage threshold is obtained. For example, with 200 μm core diameter fibre, we have increased the pulse energy that can be transmitted from ≤2 to ≥16mJ. The DOEs were designed to controllably ‘degrade’ the high beam quality (M²∽4) of the laser to a higher M² value, to match the modal distribution of the fibre being used. As an example application, we present results of laser marking trials, where the light is delivered through fibre optics with core diameters of 200 μm.