LABORATORY-BASED DIFFRACTION SIGNAL ENHANCEMENT BY THE USE OF POLYCAPILLARY X-RAY OPTICS. C. A. MacDonald, W. M. Gibson, Center for X-Ray Optics, University at Albany, Albany, NY 12222

Polycapillary x-ray optics are shaped arrays consisting of hundreds of thousands of hollow glass capillary tubes. X rays are conducted along the tubes by total external reflection at glancing incidence. Gently curved arrays can be used to redirect, collimate or focus the x-ray beams. The primary benefit provided by the use of polycapillary optics with conventional laboratory-based diffraction sources is the ability to transform x rays emitted over a large angular range into a beam with a much smaller angular divergence. The output angular divergence may be to some extent controlled by the specific system design, but is near the critical angle for total external reflection, about 4 mrad at 8 keV.

The optics can also provide significant benefit apart from collimation, by reducing background, suppressing high energy photons, and providing more convenient alignment geometries. The high energy photon suppression results from the inverse dependence of the critical angle on photon energy. Significant suppression of the K[[beta]] peak relative to the K[[alpha]] peak has been demonstrated for Cu radiation.

Insertion of capillary optics into existing diffraction systems does not provide maximum benefit compared to re-engineered system. However, preliminary measurements performed in these conditions show significant signal gains. Large area thin film diffraction signals were shown to increase by a factor of 3 to 8 when a collimating optic with a linear capture angle of 0.15 rad, 12.5um channel size, and output area of 3.1 cm was placed into a standard Bragg-Bretano diffractometer. Capillary optics provide even larger signal gains for very small samples. More than an order of magnitude signal increase was achieved for a 0.3 mm Lysosyme crystal by employing an optic with a 0.1 rad capture angle and 5 mm output diameter. This paper will present a review of the broad range of applications of capillary optics to diffraction systems.