We present an X-ray mirror bender that includes multiple spring actuators that introduce a controlled deformation of the
mirror substrate capable of correcting residual figure errors on the mirror, below one nanometer. For usual mirror
dimensions, this requires applying correcting forces with resolution and stability in the order of 0.01 N, and a range up to
20 N, depending on the initial figure error of the mirror. To obtain the required stability, the actuators need to
compensate intrinsic mechanical instabilities, such as thermal drifts or the limited repeatability of parts that move during
the adjustment of the figure. The concept we propose uses weak springs that allow reducing all these effects below
noticeable values. Additional considerations on friction and parasitic components of the force are accounted. The system
also includes two independent bending actuators with a larger force range to generate the mean elliptic figure of the
mirror. Metrology tests of the performances of the system show that the correctors are repeatable within 0.01 N, and
reach much higher resolution. A prototype of the bender has been used to correct the figure error of a 500 mm long
mirror below one nanometer (root mean square). The agreement to the predicted figure is better than 0.08 nm rms.
|