Into polarization control in laser cutting with direct diode lasers

Laser cutting of metal sheets with direct diode lasers (DDL) has recently proven to be feasible, showing industrial relevant cutting speeds at acceptable cutting quality. Further developments are still required to optimize the cutting performance of such technology before it can be considered as an alternative to CO2 or fiber laser variants. In this paper, laser polarization control is studied as a strategy to enhance the cutting performance of such lasers systems. For this purpose, two DDL sources, with output powers in the range of 750 W, have been installed in an experimental gantry platform which allows an independent control of common cutting parameters (focal point position, stand-of-distance, cutting speed, nozzle opening, gas selection, and gas pressure). Different optical designs and combinations of optical components were used to obtain a set of spatial polarization arrangements, including: linear-, cross-, azimuthal-, and radial-polarizations schemes. A series of experiments on different materials (stainless steel 304 L and 316 L and steel S355) were done to verify the influence of such configurations on laser cutting of metals with both reactive and nonreactive gases. Influence of polarization on the cutting results is found to be very high when cutting with a nonreactive gas, such as nitrogen, while the same effects are less evident when a reactive gas, oxygen, is used. Focal point position and material composition are found to significantly influence the performance obtained with the different polarization schemes. Axes of symmetry of the tested polarization strategies and directionality dependence of the cutting results are taken into account and discussed in this paper, while different strategies are proposed to improve their applicability.