Tapered monocapillary optics for synchrotron x-ray microfocusing

The use of synchrotron X-ray sources for diffraction and fluorescence analysis has permitted the study of samples with improved structure resolution and spatial resolution respectively. However, even the highly-intense X-ray spectra available using synchrotron sources may be insufficient to perform some analyses on weakly-diffracting or low-concentration samples. The available X-ray intensity per unit irradiated volume and detector noise level impose a lower limit on detection sensitivity. Even where sufficient intensity is available to make a single measurement, time constraints may still preclude diffraction data collection over sufficient reciprocal space volume or high-resolution fluorescence data collection over a large sample area. In recent years, many groups have investigated the use of monocapillary optics to produce high-brightness beams of small diameter by multiple reflection of an input X-ray beam within a tapering cylindrical bore(4.8.12). However, the low divergence of synchrotron X-rays permits the use of true geometrical focusing optics with greater efficiency than that demonstrated by multiple-reflection monocapillaries(1). We describe the use of a paraboloidally-tapered glass monocapillary to focus singly-reflected X-rays onto a small area located 40 mm from the optic. Our optics have produced intensity gain factors of 700 within a 5-mu m diameter region of the beam focus for 8 keV X-rays(2). The use of this optic in protein crystal microdiffraction and XANES and SRIXE microfluorescence analysis is also presented.