Abstract: A method of forming a complex profile of uneven depressions in the surface of the ablatable workpiece by laser ablation with the use of a simple optics or a mask of a simple configuration. The method includes the steps of determining the complex profile in accordance with a particular feature to be given to the surface of the workpiece, then dividing the complex profile into more than one simple and regular waveform patterns of different characteristics, and irradiating an energy beam to the surface of the work piece to form the individual regular waveform patterns successively in an superimposed fashion by ablation in the surface of the workpiece. Accordingly, the desired complex profile can be easily obtained at an improved efficiency and at a moderate cost.

Abstract: A method for cooling and if necessary calibrating elongate articles 7 of plastic, in which the article 7, during its continuous progress has flowing round it only a gaseous cooling medium 42 at a temperature of less than 100.degree. C. at least over a portion of its outer surface and extending over a pre-determinable length of the article 7, in a plurality of flow areas 25-35' separate from one another and located one behind the other in the extrusion direction, arrow 5.