Reducing plasma shielding effect for improved nanosecond laser drilling of copper with applied direct current

Laser drilling of copper faces challenges due to its high reflectivity and high thermal conductivity of the laser beam. To enhance laser drilling efficiency and hole surface quality, the copper substrate was applied with a direct current (DC) during a 355 nm nanosecond laser drilling process. It was found that introduction of the DC current played a noticeable role in reducing the entrance hole diameter, increasing the depth of the blind hole, decreasing the taper angle, improving the inner surface finish, and enhancing the hole integrity with less amount of debris at the hole exit. Explanation of the processing mechanism is provided by investigation effects of key processing parameters and modeling of DC current-induced magnetic field on the laser-induced plasma. The applied DC current through the copper substrate during laser drilling generated an induced magnetic field and the Lorentz force of the induced magnetic field limited the expansion of the laser-induced plasma in the direction parallel to the laser beam, which weakened the shielding effect of the plasma and thus improved the processing efficiency and hole quality of the nanosecond laser drilling. The study results may open a new path for efficient and high quality laser machining of reflective, high thermal and electrical conductive materials.