Cutting and drilling of materials, especially metals, is well-established in industry. Because laser processing is typically slower and more costly than conventional processes, it is typically used in high value applications where precision is required. These applications are important drivers for laser source development, motivating improvements in cost, throughput, and efficiency of short pulse lasers. The desire to improve the throughput and efficiency of laser drilling and cutting also drives the exploration of new approaches which optimize the laser material interactions involved in the ablation process itself.

Both pulsed and continuous wave (CW) lasers are employed in metal processing. When a laser pulse interacts with a metal surface, it vaporizes a thin (10 to 100 nm) layer of material leaving behind a melt layer. The energetic cost of removing material as a vapor is high, since much of the energy of the laser pulse goes into heating the vapor and into the enthalpy of vaporization which is in general high. Thus, short pulsed lasers have low removal efficiency. For longer pulses (nanosecond and longer) or in the case of CW excitation, in which the laser intensity is much less than for the shorter pulses, vaporization can be reduced and more energy goes to creating a deeper melt layer. The most efficient processes avoid vaporization, setting up conditions to remove material as a lower temperature melt. However, the melt is held tightly to the surrounding material by surface tension, and in deep channels created by high aspect ratio drilling, the melt can be very difficult to remove. This limitation can be overcome in some industrial processes through use of high-pressure gases, however, the effectiveness of this approach is reduced in high aspect ratio channels, for very fast drilling or cutting, for thick materials, or in cases where some stand-off is required such that the laser is not proximate to the surface.