Lasers have been used to produce high-aspect-ratio holes — i.e., holes whose depth-to-diameter ratio is much greater than 10:1 — for applications that include oil galleries in engine blocks, aerospace turbine-engine cooling holes and for scientific applications such as components used in laser fusion experiments. Depending on the application, the holes must meet criteria that include hole size, straightness and taper as well as limitations on the formation of recast and debris and the size of the heat-affected zone. (The heat-affected zone is that region where there is a change in the physical properties of the material, typically caused by thermal conduction from both the laser and laser-produced plasma.)

Very demanding applications require that high-aspect-ratio holes that are straight and have little or no heat-affected zone be produced in materials such as ceramics, semiconductors and metals. We have found that using a train of carefully timed pairs of nanosecond laser pulses — instead of a train of single laser pulses — to drill small, high-aspect-ratio holes vastly improves the results...

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