Focusing coherent x-rays with refractive optics

Refractive lenses have been used successfully to focus incoherent x-ray emission in the wavelength range from 2 to .5 Angstrom with focal lengths on the order of one meter. A stack of N lens elements is employed to reduce the focal length by the factor N over a single element, and such a lens is termed a Compound Refractive Lens (CRL). Contrary to intuition, misalignment of parabolic lens elements doesn't alter the focusing properties and results in only a small reduction in transmission. Coherent x-ray sources are being developed with wavelengths of 1-1.5 Angstrom and source diameters of 50-80 mum, and the CRL is ideally suited to produce a small, intense image. Chromatic aberration increases the size of the image and so it is important to provide chromatic correction to minimize the image dimensions. Pulse broadening due to the dispersion of the lens material is negligible. Intensity gain is in the range from 10(5) to 10(6), where gain is defined as the intensity ratio in an image plane with and without the lens in place. Maximum image intensity is obtained when the CRL is placed a distance of 100 to 200 m from the source, and the typical diameter of the focused spot is about one micron.