Laser drilling of high aspect ratio holes in copper with femtosecond, picosecond and nanosecond pulses

• Published in: Applied physics. A, Materials science & processing Materials science & processing, 2008-03, Vol.90 (3), p.537-543
• Main Authors: Weck, A., Crawford, T.H.R., Wilkinson, D.S., Haugen, H.K., Preston, J.S.
• Format: Article
• Language: English
• Subjects: Applied sciences; Blanking. Shearing; Characterization and Evaluation of Materials; Condensed Matter Physics; Cutting; Exact sciences and technology; Machines; Manufacturing; Metals. Metallurgy; Nanotechnology; Optical and Electronic Materials; Physics; Physics and Astronomy; Processes; Production techniques; Surfaces and Interfaces; Thin Films
• ISSN: 0947-8396; 1432-0630
• DOI: 10.1007/s00339-007-4300-6

Deep laser holes were drilled in copper sheets using various pulse lengths and environments. By recording the intensity on a photodiode placed under the sample while drilling the holes, we obtained the number of pulses to drill through the sheet as a function of pulse length and energy. The entrance diameter of the holes was successfully predicted using a Gaussian approximation and a material removal fluence threshold of 0.39 J/cm 2 for a pulse length of 150 fs. From cross sections of the holes, the morphology of the inside walls was observed and shows an increase in the amount of molten material with pulse length. A transition pulse length is defined as the point at which the laser affected material goes from being mainly vaporized to mainly melted. This transition occurs near ∼10 ps, which corresponds approximately to the electron–phonon relaxation time for copper.