A high precision 25-actuator optical surface bender for ultra-high resolution soft x-ray spectroscopies

To facilitate ultra-high energy resonant inelastic X-ray scattering (RIXS) and angle-resolved photoemission (ARPES) in the soft X-ray spectral region, a high precision 25-actuator optical surface bender has been designed, constructed and tested. The mechanical design of the bender is based on a novel high precision, high resolution flexure hinge adjustment system. Among the 25 actuators, 6 actuators are for controlling the surface major profile by setting positions, while the remaining 19 actuators are for fine tuning the profile by setting forces. The long trace profiler measurements show that, before bending, the intrinsic surface slope error of the flat mirror or grating is around 0.3 µrad root-mean-square (rms). By using all 25 actuators of the bender, a surface slope error as low as 0.023 µrad rms has been achieved with the surface profile set to a desired higher degree polynomial. The bender can also be used to eliminate the slope error caused by thermal deformation set off by the synchrotron radiation heat load. Based on the ray tracing simulation, gratings with an overall surface slope error better than 0.03 µrad rms are sufficient to reach an energy resolving power of 100,000 and 140,000 for RIXS and ARPES, respectively.