rate of rotation and the amount of coolant fluid flowing through the cylinders will all depend upon the power to be dissipated and upon the degree to which the beam must be clipped and confined those skilled in the art will have no difficulty in tailoring an aperture to suit their requirements with all apertures a portion of the optical flux that is to be removed from the beam will be scattered the direction of scattering depending on the relative direction of the incoming flux and the surface of the clipping member the embodiment of fig2 with a high fraction of the deflected beam being deflected in a grazing angle will tend to have the undesired radiation closer to the direction of the diverging beam than will the prior art device shown in fig1 the use of relatively small cylinders will tend to increase the angle at which the scattered radiation emerges the cylinders may be polished to a high degree of finish by diamond turning and optical polishing techniques thereby increasing the fraction of unwanted radiation which is deflected rather than being absorbed by cylinders 210 and 212 the distance 215 between the cylinders 210 and 212 may be adjusted by incorporating conventional flexible driving means and coolant means so that the distance 215 may be readily adjusted fig2 illustrates schematically i e through symbols and without conveying any spatial information a method of rotating the cylinders with belts 252 and 254 turning shafts 253 and 255 respectively power is supplied by conventional source 250 represented symbolically be a circle the spacing 215 may be adjusted by translating cylinder 210 parallel.