Machining of stainless steel and copper with ps-laser pulses and 180W of average power using DOE and synchronized scanning

Abstract

Machining of stainless steel with ultrashort laser pulses is often a challenging task due to heat accumulation problems leading to bumpy surfaces or due to the formation of cavities or cone-like protrusions (CLP) at high pulse energies. With a specific diffractive optical element (DOE) leading to a special beam shape and synchronized scanning a removal rate of 16 mm3/min was achieved on steel AISI 304 with an average power of 180 W and a repetition rate of 1 MHz. Flat and shiny surfaces without CLP's and bumps having a surface roughness of sa < 500 nm were achieved. In case of copper the maximum removal rate amounted 17 mm3/min with a surface roughness of sa < 400 nm at a repetition rate of 400 kHz and an average power of about 150 W. The experiments clearly show, that with beam forming high average powers can be used for high quality laser micromachining with ultrashort laser pulses and single beams at average powers exceeding 100 W.