Surface metrology of cylindrical mirrors with sagittal curvature in low spatial frequency range

摘要

Side-deflecting cylindrical mirrors with sagittal curvature horizontally deflect and focus the beam in the vertical direction. This optical scheme applied to fourth-generation synchrotron light source beamlines has potential advantages leading to nearly aberration-free focus and variable beam size or focus position. We characterize the surface quality of sagittal cylinders in the low spatial frequency range with the long trace profiler (LTP) and the Fizeau interferometer (FZI). In the standard LTP, the sagittal curvature of the cylindrical mirror causes the reflected laser beam to diverge, which consequently shifts the focus out of the detector plane, turning a reliable measurement impossible. Therefore, a positive cylinder lens is placed at Cat's eye position to recollimate the beam. In this paper, we describe the alignment procedure and define the required accuracy of each degree of freedom for both the cylinder lens and the cylindrical mirror to be characterized. Measurements with the FZI arc limited to optics with small curvatures when measuring with a flat reference. We show that measuring a sagittal cylinder slightly out-of-focus overcomes this limitation. Measurements with the FZI also allow to characterize the deformations caused by clamping forces due to fixation. We compare the measured deformation with Finite Element Analysis (FEA) simulation results. We present measured surface height and slope profiles (LTP and FZI) of cylindrical mirrors for SIRIUS beamlincs.