Monocapillary Optics Developments and Applications

Hollow glass tubes are in use at Cornell High Energy Synchrotron Source (CHESS) as X-ray optics in the 4 to 25 keV range to take large diameter, fairly parallel X-ray beams and compress them into smaller diameter, more divergent beams for various kinds of X-ray applications. The optics come in two forms: 1) multibounce condensing capillaries for making submicron diameter beams and 2) one-bounce imaging capillaries with working distances of 20 to 50 mm from the tip of optic to the focal spot. The preliminary results of the applications, from X-ray fluorescence imaging to protein crystallography, are briefly described in this paper. INTRODUCTION It has been demonstrated by a number of research groups and companies over the last decade that hollow glass capillaries (operating at glancing angles by total reflection from their inner walls) are very useful focusing optics in synchrotron X-ray instrumentation [1-4]. Generally speaking, the polycapillary forms [5-7] are most useful for beam sizes greater than 40 microns and the monocapillary forms are especially good for micron sized beam applications [8-15]. There is strong overlap of the two types of optics for sizes between 1 and 40 microns. By using glass capillaries, one can create a smaller beam size as well as increase the X-ray intensity per unit sample area. There are basically two different kinds of monocapillaries: condensing and imaging. In this paper we will first describe the state of condensing capillary developments and applications at CHESS and then discuss the imaging capillary progress. CAPILLARIES DEVELOPED AT CHESS For a condensing monocapillary, the X-rays passing through may be reflected many times by total reflection from the hollow inner wall of the capillary before they pass out the tip, as shown in figure 1. The X-ray beam size produced by a condensing capillary is mainly dependent on the opening of the capillary tip and not strongly related to the capillary figure. Therefore it is relatively easy to make sub-micron scale X-ray beams for experiments. One condensing capillary developed at CHESS and currently available for users has a 0.8 micron opening at the tip, a 50 micron opening at capillary base entrance, and a length of 223 mm. For an imaging capillary, all rays will be focused into a single focal point at some distance beyond the tip as shown in figure 2. The focal spot size of a one-bounce capillary is basically a demagnified image of the synchrotron source blurred out slightly from small residual slope errors from capillary manufacture. This size is not directly related to the capillary tip opening. The elliptical shape chosen depends on the capillary manufacture accuracy, required focal spot size, maximum focal divergence allowed, working distance and X-ray source parameters [16]. We Copyright©JCPDS International Centre for Diffraction Data 2003, Advances in X-ray Analysis, Volume 46. 320