X-ray tests of microfocusing mono-capillary optic for protein crystallography

A single, borosilicate-glass capillary was drawn into a 30.5 cm long elliptical shape. The inside diameter was 0.40 mm at the large base end and 0.13 mm at the tip. With 12 keV X-rays from the CHESS D1 bending magnet, the single-bounce capillary produced a focus of better than 18 μm in diameter (FHWM) at a 3 cm distance from the capillary tip. A flux gain of 110 in the focus position was observed along with a total flux in the spot of 4×1010 X-rays/s (conditions: 5.3 GeV, 182 mA, 1.5% bandwidth multilayer, 12 keV X-rays). A measurement of the far field focus ring diameter yielded a divergence of 3.8 mrad, in good agreement with the 4 mrad design of the optic for protein crystallography. Using a small 25 μm square beam, we measured the local reflectivity to be greater than 95% and the inner slope errors of the capillary to average about ±150 μrad, both from raw and elliptically shaped tubing. Our conclusion is that more perfect starting tubing (i.e. one with lower slope errors) is needed to make even more perfect elliptically figured optics in the future.