Drilling of aluminum and copper films with femtosecond double-pulse laser

• Drilling process and hole morphology change with double pulse delay.
• Redeposited material diameter behaves differently for aluminum and copper.
• Plasma shielding and liquid phase coupling are responsible for drilling rate change.
• Oxidation and electron–phonon coupling result in difficult drilling of aluminum.
• An oscillation pattern of drilling efficiency is observed.

Aluminum and copper films are drilled with femtosecond double-pulse laser. The double-pulse delay is scanned from −75 ps to 90 ps. The drilling process is monitored by recording the light transmitted through the sample, and the morphology of the drilled holes is analyzed by optical microscopy. It is found that, the breakthrough time, the hole evolution during drilling, the redeposited material, the diameters of the redeposited area and the hole, change as functions of double-pulse delay, and are different for the two metals. Along the double-pulse delay axis, three different time constants are observed, a slow one of a few tens of picoseconds, a fast one of a few picoseconds, and an oscillation pattern. Results are discussed based on the mechanisms of plasma shielding, electron–phonon coupling, strong coupling of laser with liquid phase, oxidation of aluminum, laser induced temperature and pressure oscillations, and the atomization of plume particles.