Patent Number: 
Section: description

It is desirable in x-ray and neutron optics to use polycapillary optics to collect a diverging or parallel x-ray or neutron beam and convert the beam into a converging, parallel or diverging beam. Multi-fiber polycapillary optics include one or more polycapillaries positioned so that along their length they have a required profile for this purpose. A new design is presented herein for the manufacture of polycapillary optics. The design utilizes, in one embodiment, a one-piece support device 20 incorporating one or more internal bores that may have a constant or varying diameter so that a central opening or passageway 22 is defined as shown in FIG. 2. Within the inner surface of support device 20 defining the central opening, multiple locating structures 26 are defined for accommodating polycapillary positioning components as shown in FIG. 3. The central opening 22 has a central axis 23 that is used to align the positioning components. The use of a single axis 23 for alignment is significant because it eliminates the five degrees of freedom arising from the two-axes alignment approach described under the Background of the Invention. Also, many of the tolerance buildups are eliminated because the screens are aligned to the inside surface of support device 20 about the defining central axis 23, thereby eliminating tolerances associated with positioning holes 10 (FIG. 1) needed to align the screens to the screen holders and the holes for the rods 12 (FIG. 1) in the prior art approach. In one embodiment, the locating structures may comprise shoulders formed on the inner surface of housing 20 at discrete positions along the axis of central opening 22 for facilitating placement of screens 30. Those skilled in the art will note that other locating structures could be employed in place of the shoulders depicted in FIG. 2. For example, discontinuous steps or lips could be provided, as well as channels formed circumferentially within the housing about the central opening. The support structure 20 may further include placement holes 24 for springs or other fastening means (not shown) on the side and/or on the bottom of the support structure to allow for positioning and alignment of the optic including translation and tilt. FIG. 3 depicts one embodiment of positioning component 30. The positioning components, which typically comprise screens, are fabricated by photochemical machining, laser machining, electron discharge machining, or other fabrication process. Preferably, one or more polycapillary positioning holes 32 in the positioning components are fabricated at the same time, i.e., intrinsic to the nature of the process, thereby reducing positional errors. The screens are made using a fabrication process that decreases misalignment of the polycapillary positioning holes. As an example, photochemical machining, sometimes referred to as chemical milling or chemical etching, is a technique for manufacturing high-precision flat metal parts by chemically etching away the unwanted materials, using a photographically prepared mask to protect the metal that is to remain after the etching process. For the positioning components described herein, a mask can be made where the hole positions for the polycapillaries are left exposed, a resist is placed on the metal and the mask protects the metal around the holes. The holes are chemically etched, leaving only the metal surrounding the holes. This approach allows the position of the inner (hexagonal) holes 36 to the exterior periphery 38 of the part to be tightly controlled. The assembly disclosed herein advantageously utilizes this tightly controlled tolerance from the interior hole positions to the exterior periphery of the positioning component as a means to control the fiber hole positions in the final assembly. As shown in FIG. 3, unitary support device 20 accommodates positioning components 30 against locating structures 26 interfacing with internal opening 22. This design eliminates the stack-up errors that are inherent to the conventional polycapillary optic construction approach. Within the unitary structure 20, locating shoulders, steps, channels, openings, or other techniques could be used to locate the polycapillary positioning components of the assembly. Because these locating structures are precisely machined into the unitary frame, more exact placement of the polycapillary positioning components is achieved. In one specific example, the bore depth through housing 20 can be varied at predefined locations in order to create shoulders for receiving the positioning components and thereby control spacing along the optical axis between the different positioning components. The outer shape of the support device 20 is non-critical relative to alignment of the polycapillary (glass) fibers. Hence the housing can be round, square or any other desired shape. Further, high precision tolerances are not critical to the outer profile. The more significant aspect is the inner bore configuration and depth that is used to create the locating structures to precisely locate the fiber positioning components. As noted, the inner bore diameter of the housing can be used for locating the fiber positioning components relative to one another. For example, the bore depth can be varied as the central opening is being formed within the housing in order to create retaining steps at predefined positions within the housing. Further, in one embodiment, the diameter of the central opening could be adjusted to narrow with the formation of each retaining step within the housing (see FIG. 5 showing in cross-section two different diameters A, B of the central opening). Because the holes are bored into the mono-frame support structure, the stack-up error associated with a multiple part assembly is reduced. In the embodiment shown in FIGS. 2 and 3, the mono-frame support structure 20 uses a series of four coaxial bores 22 machined in one operation to establish the locating structures 26 for the polycapillary positioning components 30. A machining operation (such as boring or plunge electron discharge machining) yields a much tighter control on the positioning component alignment and the spacing between positioning components than the approach of FIG. 1. Although not shown, each screen of the positioning component could be supported by one or more disc supports that provide stiffness to the positioning component close to the edge of the fiber positioning holes. In the depicted embodiment, four positioning components 30 are attached to support structure 20. The positioning components are supported by frames. Each frame/positioning component assembly is placed (and adhesively secured) into position at the appropriate location, i.e., at the appropriate locating structure. The positioning components may be placed into the support structure from the side or through the inner bore openings. Each positioning component is aligned relative to the first positioning component that is placed in the inner core to avoid rotation of the positioning components relative to one another. FIG. 4 depicts an example of two different positioning components 32 and 34 for use within a polycapillary optic assembly in accordance with the principles of the present invention. In this example, the spacing between openings 36 in positioning components 32 and 34 is varied relative to the outer perimeter 38 of the screen. This arrangement might be used if the optic assembly is to collect a parallel beam at its input (left side) and convert it to a focused beam at its output (right side). Those skilled in the art will note that by varying the positioning components (30) within the housing, different polycapillary optics can be readily assembled. Specifically, polycapillary optics can be assembled for a parallel source, a diverging source, or a converging source, and similarly, optics can be assembled to produce a collimated, converging, or diverging beam. For a polycapillary optic to accept diverging radiation and output converging radiation, the first and last locations of positioning components within the housing determine the input and output focal distances. Thus, the orientation of the polycapillary fibers at these positioning components is significant to fabrication of the optic with the desired input and/or output focal distance. Similarly, for an optic accepting parallel radiation, the location of the last positioning component is significant. For an optic accepting diverging radiation and outputting converging radiation, the location of the first positioning component is important. Variables to be controlled might include internal bore diameters, the concentricity of the inner core frame, and the required tolerance level associated with the positioning component manufacture. For example, in one preferred embodiment, the positioning components can be manufactured at different tolerance levels for the location of the fiber positioning holes (32) relative to the outside circumference of the positioning component (30). An acceptable tolerance can range from 1 to 100 microns. Associated with the positioning component tolerance improvements are substantial cost considerations. The tolerance level of the boring operation, and manufacturing tolerances of the positioning components can be varied as needed in order to meet different performance criteria of the optic. Those skilled in the art will note that the support device and polycapillary optic assembly presented herein can be produced for a wide range of optic sizes, for example, for optics from a diameter of 500 xcexcm to 1 meter, and with a length varying from 2 mm to 2 meters. While the invention has been described in detail herein in accordance with certain preferred embodiments thereof, many modifications and changes therein may be effected by those skilled in the art. Accordingly, it is intended by the appended claims to cover all such modifications and changes as fall within the true spirit and scope of the invention.