Imaging properties of beam line optics for undulator based third generation synchrotron facilities

Beam line optics for synchrotron facilities are generally designed from geometric calculations wherein the bending magnet, undulator, or wiggler photon source is approximated by a high divergence point source. In this article we will, however, show that in the case of a synchrotron radiation source with very small divergence (such a source can be encountered at an undulator based third generation facility) the imaging properties resemble those of a laser source. This implies certain criteria for the focusing properties of the optical elements in the beam line. For instance, a beam waist is found close to the back focal plane of the optical element, with its position and size dependent on the divergence. If the divergence is determined predominantly by the diffraction part, this also means that the size and position of the beam waist is photon energy dependent. The study has been carried out by analytic treatment, numerical simulations as well as beam profile measurements carried out at beam line 1511 at the MAX II synchrotron in Lund, Sweden.