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Small KB Mirror System*

The IDT Small KB Mirror is based on a well established approach of dynamically figuring the mirror shape by applying two adjustable moments to a trapezoidal shaped mirror.  By correctly tapering the longitudinal width of the mirror and applying a linear moment distribution a nearly perfect approximation to the ideal focusing ellipse can be achieved. The slope errors from bending are negligible, well under 0.1μrad (typically <0.05µrad) and the mirror surface given a properly designed bender can be formed to nearly perfect ellipses.

Successful dynamically figured optics requires bending mechanics that are capable of precisely applying a linear moment distribution without causing residual distortions or drifts in time due to temperature variations and system relaxations.  The IDT Small KB Mirror bender is designed to apply only the minimum force necessary to achieve the required figure resulting in maximum useful mirror length and avoiding distortions caused by benders that clamped to the mirror.  The bender is designed to utilise mirrors with simple shapes that are easy to install and capable of accepting a range of mirror thicknesses and tapers.  This approach reduces the cost for manufacturing the mirrors and provides rapid flexibility so that a single system can be reconfigured to optimally provide focusing for a wide range of experiments.

The upstream and downstream moments are applied through the use of a crossed arm arrangement where the forces applied to the lever arms are achieved by pushing off the back surface of the mirror on opposite ends.  This results in a closed loop force system that insulates the mirrors figure from external thermo-mechanical variations in the support mechanism.  The lever arms are parallel to the length of the mirror and the applied actuator forces are perpendicular to the lever arms effectively de-coupling thermal expansion effects of the lever arms from the applied moment.  The lever arms couple to each end of the mirror through a pair of leaf springs and inner and outer bending bars. The leaf springs de-amplify thermo-mechanical drifts of the crossed arms and actuators and allow the mirror contacts to conform to the natural shape of the mirror, keeping residual contact stresses to a minimum.

The moments are controlled with two stepper motor and gear head combinations.  The actuators utilise a scissor jack arrangement that results in a constant stepper motor torque as a function of bending moment keeping the systems drive friction independent of radius of curvature and allowing fine figure adjustability at high bending load.  The actuators are capable of adjusting figure to one part in 104 of the final curvature which is sufficient to achieve figure errors under 0.1μm.

Small KB Mirror System Small KB Mirror System - helium version Small KB Mirror System - vacuum version

​* developed by IDT with a grant from the North West Development Agency

Small KB Results

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Technical Data