Copper vapor laser high aspect ratio drilling process on transparent materials

In this work we will present a peculiar effect induced by copper vapor laser radiation that can suggest interesting material processing applications: drilling of very long holes with very high aspect ratio in a variety of materials. In the experiments we tested some samples of transparent materials such as fused silica and glass substrates. The beam quality was improved by unstable resonators, giving an average power of 2.5 W on both emission lines with a divergence of 120 micro-rad. By tightly focusing, power densities in the range 5 - 50 GWatts/sq cm were reached. In these conditions we observed a novel drilling effect: a very long hole was produced into the sample, composed by a scarred crater of about 100 microns in diameter at the bottom on sample surface, followed by a very clean and slightly conical channel with an initial diameter of 40 microns and an aspect ratio which exceeds 50. The drilling is self-terminating in less than a second. The channel, extending well beyond the beam waist length, is regular and translucent. Our present explanation assigns the process triggering to a nonlinear enhancement of the absorption, and its subsequent evolution to the over position of several effects originated by a proper combination of average power, repetition rate and pulse peak power.