Thin-film PZT actuator performance in adjustable X-ray optic segments

Many current outstanding questions in X-ray astronomy were addressed by Lynx, an observatory concept that concluded its study phase in 2019. High-effective area, high angular resolution X-ray missions like Lynx require thin (≤ 0.5 mm thick) mirrors with precise surface figures to maintain high angular resolution (≤ 0.5 arcsec). To study methods of meeting these requirements, adjustable X-ray optics have been fabricated with thin-film piezoelectric actuators to perform figure correction. These adjustable X-ray optics serve to correct low spatial frequency figure errors (> 0.1 mm⁻¹). The fabrication and actuator performance for an adjustable X-ray mirror that forms a conical approximation to a Wolter-I telescope are reported. This mirror has a BCB insulating layer with a top level of Ti traces to address its 288 actuator cells. The individual responses of cells are measured and on average they induce a figure change of 0.87 µm peak-to-valley (PV) with an associated root mean square (RMS) of 0.10 µm. These measured cell responses are compared to predicted responses generated using a finite-element (FEA) analysis algorithm. On average the measured and predicted cell responses agree to within 0.06 µm RMS. The disagreement between predicted and measured cell responses is posited as being due to differences in radial constraints points between the FEA model and the as-built mirror mount.