The random walk of a drilling laser beam

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Abstract
Holes were drilled through 330‐μ‐thick single‐crystal sapphire wafers with a pulsed laser beam. The hole exit positions on one face of the wafer were found to have undergone a random‐walk displacement relative to the entrance hole positions on the opposing face of the wafer. This random displacement increased with the number of laser pulses required to drill through the wafer. A model in which the bottom of the drill hole experiences small random displacements during each laser pulse was used to describe the experimental observations. The model indicates that the average random displacement caused by each laser pulse is only a few percent of the hole diameter. Laser‐drill‐hole wandering can be minimized by using as few laser pulses as necessary to drill through the sapphire wafers while at the same time avoiding the cracking and spalling of the wafer that occur with a hole drilled through the wafer with a single pulse.

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