Effects of laser operating parameters on metals micromachining with ultrafast lasers

180 femtoseconds (1 kHz) and 10 picoseconds (1-50 kHz) ultrafast laser micro-structuring of the metals Ti alloy, Al and Cu have been studied for the purpose of industrial application. The effects of some key laser operating parameters were investigated. The evolution of surface morphology revealed that laser pulses overlap in a range around the spatial FWHM can help to achieve optimal residual surface roughness. While observed ablation rate (unit: μm3 per pulse) changed dramatically with repetition rate due to the combined effects of plasma absorption, residual thermal energy and phase transition, higher throughput can be achieved with higher repetition rate. This study also indicated that residual surface roughness is almost independent of repetition rate at 10 ps temporal pulse length. The ablation depth is approximately proportional to the number of overscan; however, machining accuracy deteriorates, especially for femtosecond laser processing and metals with low thermal conductivity and short electron-phonon coupling time.