Two-foci bendable mirrors for the ALS MAESTRO beamline: design and metrology characterization and optimal tuning of the mirror benders

MAESTRO, the Microscopic and Electronic STRucture Observatory, currently under construction at the Advanced Light Source (ALS), will be a world premier facility for the study of electronic and structural properties of in situ grown crystals. The new facility will be comprised of several end-stations, including angle-resolved photoemission spectroscopy, μARPES and nARPES end-stations, and a photoemission electron microscope combined with a lowenergy electron microscope (PEEM/LEEM). Redirection of the x-ray beam between the μARPES and PEEM/LEEM end-stations, which are longitudinally separated by 2.5 meters, uses a system of two bendable mirrors, placed in Kirkpatrick-Baez configuration designed for two foci. Here we present the details of the mirrors’ design and report on the characterization of the mirrors carried out at the ALS X-ray optical laboratory (XROL). Optimal tuning and calibration of the mirrors was performed using a technique recently developed at the OML [Opt. Eng. 48(8), 083601 (2009)]. The technique is based on regression analysis of surface slope data obtained with a long trace profiler (LTP). We provide results of tests of temporal and temperature stabilities of the shape of the mirrors. High reliability of the optical metrology with the mirrors has become possible due to a modification of the tuning procedure described in the present article. The modification allows accounting for the gravity sag effect, as well as the LTP systematic error in measurements with significantly curved x-ray optics.