For focusing of the X-ray beam, ID11 has an in-vacuum transfocator (IVT). This operates by inserting lenses into and out of the beam via pneumatic actuation. The lens positions are determined by a high precision mount; therefore it is easy to insert and remove lenses as desired during an experiment. This makes such a device very attractive for performing experiments where variable beam size might be desired.

The transfocator consists of 8 cylinders with 1, 2, 4, 8, 16, and 32 Be lenses, 32 and 64 Al lenses, and one pinhole (10 x 10 microns). By combining these sets of lenses it is possible to focus throughout the entire energy range in EH3, and up to 70 keV in EH1. Furthermore, the depth of focus in EH3 at ~95 m is sufficient that any energy can be used without translation along the beam being necessary. In EH1, it is necessary to translate along the beam unless certain energies are selected.

a) In vacuum transfocator and b) engineering drawing, located in the optics hutch at ID11.

In the first experimental hutch (EH1), at 41 - 44 m from the source, the transfocator can be used to microfocus in the range of ~25 - 75 keV, producing spots on the order of 6 x 45 μm2. For the end station (EH3) at 95 m, the smallest focal spot currently produced is on the order of 50 x 220 μm2.

Schematic showing the IVT located in OH1. This can give a 3:1 or 1:2 focusing of the source, depending on which experimental hutch (i.e. distance) is being used. Image from Vaughan et al. 2011.

The transfocator is also commonly used as a condenser for post focalization. The small beam size produced corresponds well with the acceptance aperture of some of the downstream nano-focusing optics (see the secondary optics page). Coincident focusing can produce substantial flux increases but also beam broadening, however collimation or underfocusing can limit this affect.

A further interesting characteristic of using refractive lenses for focusing/pre-focusing is that the focusing of the lenses is chromatic, so that only a single energy is focused at a given distance, as opposed to typical periodic monochromators such as crystals and multilayers, in which higher order reflections diffract multiples of the fundamental energy. This gives the useful side benefit of suppression of harmonics in the focused beam.This characteristic also means that the transfocator can be used without any other optics as a longitudinally dispersive focusing monochromator, with a band pass proportional to the focal length.

If a pinhole is placed as a secondary source at the focal position, a very high flux beam can be produced. Such ultra intense, stable and focused moderate band pass beams can be useful for several applications in which high energy resolution is not necessary, such as scattering from liquids or poorly crystalline materials, or for many imaging applications, particularly when very high time resolution is needed.

ID11 has a second transfocator on the beamline, an in-air transfocator (IAT). This is located 92 m from the source, in Optics Hutch 2.

For a fuller descripition of the workings of compact refractive lenses follow this link to the  Institute of Physics B of the RWTH Aachen University. From this page there can be found a Java application for the calcualtion of focal distance is based on the paper of Lengeler et al. (1999).

  • Vaughan, G. B. M., J. P. Wright, A. Bytchkov, M. Rossat, H. Gleyzolle, I. Snigireva, and A. Snigirev, 2011, X-ray transfocators: focusing devices based on compound refractive lenses: Journal of Synchrotron Radiation, v. 18, p. 125-133.
  • B. Lengeler, C. Schroer, J. Tümmler, B. Benner, M. Richwin, A. Snigirev, I. Snigireva, M. Drakopoulos, "Imaging by parabolic refractive lenses in the hard X-ray range," Journal of Synchrotron Radiation 6 (6), 1153-1167 (1999)