Preliminary tests of an X-ray Michelson interferometer

A Michelson interferometer has been proposed as a diagnostic tool for measuring the longitudinal coherence of X-rays from seeded FEL undulators [1]. In the authors’ contribution to last year’s HASYLAB Annual Report [2], a design for an X-ray Michelson interferometer was described and the earliest successful test of it was shown. The Michelson interferometer is based on the BBB interferometer of Bonse and Hart [3]. It is built into a single silicon crystal into which an LLL interferometer [4] was also cut. One of the BBB interferometer’s mirrors is connected to the rest of the crystal through a set of flexure joints, so that a piezo pressed against it can displace it perpendicular to the other components of the BBB and so introduce a path difference. At the end of the article, two tasks were set forth: the continued examination of the interferometer with brighter sources than the bending magnet ROMO-1, and the development of a piezo system capable of introducing the necessary displacement in the movable mirror. The past year’s results in both these tasks will be outlined here.