Abstract
Piezoelectric bimorph deformable mirrors (`bimorphs') are routinely used on many synchrotron and free-electron laser beamlines to provide active variation in the size and shape of the X-ray beam. However, the time-domain potential of such optics has never been fully exploited. For the first time, the fast dynamic bending response of bimorphs is investigated here using Fizeau interferometry. Automated scripts for acquisition and analysis were developed to collect Fizeau data at a rate of 0.1 Hz to record dynamic changes in the optical surface as voltages were applied to the electrodes of the piezoelectric actuators. It is demonstrated that residual drift in the tangential radius of curvature of a bimorph can be significantly reduced using enhanced opto-mechanical holders and a fast programmable high-voltage power supply. Further improvements are achieved by applying small opposing voltages to compensate for piezoelectric creep. The present study shows that bimorphs can truly be used as high-speed adaptive optics for the X-ray domain, even without closed-loop feedback correction. This opens the possibility for relatively simple real-time tuning of the profile of X-ray bimorphs. Part II of this study [Alcock, Nistea, Signorato, Owen, Axford, Sutter, Foster & Sawhney (2019), J. Synchrotron Rad. 26, 45-51] builds upon these results and demonstrates how bimorphs can rapidly provide customisable sizes and shapes of synchrotron X-ray beams, specifically tailored to suit the experimental samples being investigated.
Highlights
Since their initial development for X-ray applications in the mid-1990s (Susini et al, 1996; Signorato et al, 1998), piezoelectric bimorph deformable mirrors (‘bimorphs’) have been widely used at many synchrotron radiation and X-ray freeelectron laser (XFEL) facilities to focus X-ray beams
The mirror substrate bends when voltages are applied to the piezo ceramics via each electrode
For the first time, using ex situ metrology feedback from a Fizeau interferometer, we investigate the dynamic evolution of the optical surface of several microfocusing bimorphs and determine whether they can be driven at higher speeds without causing residual curvature drifts
Summary
Since their initial development for X-ray applications in the mid-1990s (Susini et al, 1996; Signorato et al, 1998), piezoelectric bimorph deformable mirrors (‘bimorphs’) have been widely used at many synchrotron radiation and X-ray freeelectron laser (XFEL) facilities to focus X-ray beams. It was hypothesized that such drifts were caused by mechanical holders and stiff electrical connectors that were resisting the action of piezo bending This accumulated elastic energy is either gradually released over several hours or days in a continuous manner or via a series of discrete steps through stick/slip frictional behaviour. Small changes in the size of the focused X-ray beam, that were once hidden by the intrinsic blurring caused by optical slope errors, are becoming increasingly evident due to the sharper focus provided by super-polished substrates. Once such X-ray beam drifts become routinely observable, this motivates the study of their time-domain behaviour to mitigate the risk of reduced beamline performance. In the follow-up paper (Part II; Alcock et al, 2019) we build upon these results to present a proof-of-principle beamline experiment showing how microfocus bimorphs are capable of high-speed control of the size and shape of a synchrotron X-ray beam
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