Simple method for focusing x rays using tapered capillaries.

A new method of focusing x rays is described using appropriately tapered capillaries. The x rays are incident on the inner surface of the capillary below the critical glancing angle and reflect due to total external reflection. By appropriately narrowing the capillary, the x rays can thus be focused in a broad band of energies. The theory of the effect and optimum taper is described. A measurement verifying the focusing capability of the method is presented. The method appears practical for focusing bending magnet synchrotron radiation around 8 keV down to a diameter of 10 mum from an initial dimension of 1-mm(2) incident cross section with an attenuation of the total energy of ~2, i.e., an increase in the intensity per unit area of 6.5 x 10(3). Greater focusing is possible with softer x rays and from undulator sources. The wide-ranging applicability of the technique is discussed.