the filter 6 so that only the ultraviolet light 12 is transmitted as is shown for image plane d the uv beam formed has an approximately trapezoidal intensity profile 20 with slightly curved sides while the base line of the trapezoid is larger than the top line by an amount which corresponds to around twice the walk off in the center part of the cross section there is a roughly square section of around 500 by 500 square micrometers with homogeneously uniform energy density the lens 7 images the image plane d in enlarged form onto the surface of the pattern generator 8 image plane e which is uniformly illuminated with the square section of the homogeneous energy density only a small proportion of the uv beam 39 s energy of around 5 to 10 percent below the side lines of the trapezoid is lost in the illumination the pattern generator 8 with its lenses of short focal length shapes the desired beam pattern in which all the spots have approximately the same intensity a further lens 9 images the focal points of the lenses of the pattern generator 8 into infinity in the image plane f the parallel beam has the desired cross sectional pattern 23 with the profile 24 of the same energy densities in the spots of the pattern this beam is then imaged as can be seen in fig2 onto the sample in reduced size via the appropriate optics due to the exponential decrease of the energy density in the infrared beam 10 within the conversion crystal 4 the cross section 17 of the green light has a trapezoidal profile 18 with slightly curved side lines this shape and the process of reverse compensation in the conversion crystal 5 results in the cross section 19 of.