Kirkpatrick-Baez elliptical bendable mirrors at the Nanospectroscopy beamline: metrological results and x-rays performance

摘要

Two bendable elliptical cylinder mirrors arranged in a Kirkpatrick-Baez (KB) geometry are installed at the Nanospectroscopy beamline at ELETTRA for refocusing soft x-rays provided by an APPLE II type undulator. This achromatic focusing device delivers the beam to a micrometer-scale, high photon density spot, which is the source for a Spectroscopic Photoemission and Low Energy Electron Microscope (SPELEEM). A similar second pair of KB mirrors will refocus the monochromated light in a second experimental station for a different imaging microscope. These four mirrors, developed by S.E.S.O., are manufactured from Glidcop~(TM) in a U shaped design with 380mm length. They are electroless nickel plated for polishing and are bent into an elliptical shape applying two unequal end moments. They have been tested in the optical metrology laboratory of ELETTRA using an in-house modified version of the Long Trace Profiler (LTP): the surface slope variation as a function of the bender actuators has been measured to characterize the behavior of the bender mechanism and the accuracy of the elliptical profiles that can be achieved. Both metrological optical data and x-rays performances show the achievement of a microradian accuracy for the different profiles in which each mirror can be bent and the possibility to vary the focal distance by about 30-40% around the nominal value.