Two-plane focusing of 30 keV undulator radiation

An imaging experiment using a two-plane focusing refractive lens made of aluminium and operated in the hard X-ray range is described. The lens is made of a series of 1 and 0.8 mm-diameter lenses drilled through a 2 mm aluminium plate. It is exposed to the white beam from an undulator with total power as high as 1.7 kW and normal-incidence power density of 100 W mm(-2). The measured r.m.s. size of the image is 0.12 x 0.06 mm at a photon energy of 30 keV. Theoretical estimates for the transmission, aperture and tolerance of alignment of such lenses are made. It is found that the aperture of the lens is dominated by photoelectric absorption (Compton scattering) in the low (high) energy range of the spectrum. Beryllium is the most promising material.