Imaging by parabolic refractive lenses in the hard X-ray range

The manufacture and properties of compound refractive lenses (CRLs) for har d X-rays with parabolic profile are described. These novel lenses can he: u sed up to similar to 60 keV. A typical focal length is Im. They have a geom etrical aperture of 1 mm and are best adapted to undulator beams at synchro tron radiation sources. The transmission ranges from a few % in aluminium C RLs up to about 30% expected in beryllium CRLs, The gain (ratio of the inte nsity in the focal spot relative to the intensity behind a pinhole of equal size) is larger than 100 for aluminium and larger than 1000 for beryllium CRLs. Due to their parabolic profile they are free of spherical aberration and are genuine imaging devices. The theory for imaging an X-ray source and an object illuminated by it has been developed, including the effects of a ttenuation (photoabsorption and Compton scattering) and of the roughness at the lens surface. Excellent agreement between theory and experiment has be en found. With aluminium CRLs a lateral resolution in imaging of 0.3 mu m h as been achieved and a resolution below 0.1 mu m can be expected for beryll ium CRLs. The main fields of application of the refractive X-ray lenses are (i) microanalysis with a beam in the micrometre range for diffraction, flu orescence, absorption, scattering; (ii) imaging in absorption and phase con trast of opaque objects which cannot tolerate sample preparation; (iii) coh erent X-ray scattering.