Large-aperture compound refractive lenses

Abstract

We have measured the intensity profile and transmission of x-rays focused by a series of bi-concave parabolic unit lenses fabricated in lithium and beryllium. For specified focal length and photon energy, lithium and beryllium compound refractive lenses (CRL) have a larger transmission, aperture size, and gain compared to aluminum, epoxy, and kapton CRLs. One Li CRL was composed of 335 bi-concave, parabolic unit lenses, each with an on-axis radius of curvature of 0.95 mm. This Li CRL achieved a 95 cm focal length at 8 keV with an effective aperture of 1 mm, an on-axis (peak) transmission of 26 %, and an on-axis intensity gain of 18.9. The beryllium compound refractive lens was composed of 160 bi-concave unit lenses, each with a radius of curvature of 1.9 mm. The Be CRL achieved two-dimensional focusing at 6.5 keV with a gain of 1.5, peak transmission of 9 %, focal length of 93 cm, and an effective aperture of 600 μm. Based upon the principle of spontaneous emission amplification in an FEL wiggler, coherent x-ray sources are being developed with wavelengths of 1-1.5 a and source diameters of 50-80 μm, and the Be and Li CRL may be used to provide a small, intense image. For these coherent x-ray source parameters, the large apertures of Be and Li CRLs enable intensity gains of 10 5 to 10 6 .