Critical performance aspects of ultrashort pulse laser materials processing at high repetition rates and average powers

An experimental investigation is presented on the ultrashort pulse laser drilling of different metals with diverse thermal properties in the high repetition rate and high average power regime. An Ytterbium-doped fiber CPA system was used, providing pulse energies and repetition rates up to 70 ?J and 1 MHz, respectively. It has been found that at a few hundred kilohertz particle shielding causes a decrease of the ablation rate, depending on the pulse energy. At higher repetition rates, the heat accumulation effect overbalances particle shielding, but significant melt ejection affects the hole quality. The influence, in this regime, of pulse duration (800 fs to 19 ps) and wavelength (1030 nm and 515 nm) on the drilling efficiency and on the achievable precision have been further experimentally studied.