Marking of a workpiece by light energy

Abstract

The known technique of marking (including machining) a workpiece by light energy, e.g. a pulsed laser beam, in order to create a pattern of marks on the workpiece is improved by converting a primary beam into a plurality of individual beamlets that are arranged in an array corresponding to the desired pattern and are each focused independently of the other beamlets. This independent focusing enables the size and energy density (and hence the marking effect) of each beamlet when it strikes the workpiece to be dependent on the relative location of the workpiece and the respective beamlet, while being independent of the size of the overall pattern. This feature enables variation of the ratio between the pitch between individual marks (which determines the size of the overall pattern) and the size of each mark, and hence selection of the optimum value of this ratio for a given situation. As a result, a pattern of a chosen size can be made using a primary beam of lower power than has previously been possible, or alternatively, the same beam power can be used to make a larger mark. In another aspect the invention provides for utilization of the previously wasted energy of those beamlets not used to form the patterned array, by redirecting these beamlets either to reinforce one or more of those beamlets that do form the array or to form a second pattern of marks on the workpiece.