Several proposed future X-ray missions will 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. The fabrication and actuator performance for an adjustable X-ray mirror that forms a conical approximation to a Wolter-I telescope are reported. The individual responses of actuator cells were measured and shown to induce a figure change of 870 nm peak-to-valley on average. These measured responses were compared with predicted responses generated using a finite-element analysis algorithm. On average, the measured and predicted cell responses agreed to within 60 nm root mean square. A set of representative mirror distortions and the measured cell responses were used to simulate figure corrections and calculate the half-power diameter (HPD, single reflection at 1 keV) achieved. These simulations showed an improvement in 4.5 to 9 arcsec mirrors to 0.5 to 1.5 arcsec HPD. The disagreements between the predicted and measured cells’ performance in actuation and figure correction were attributed to a high spatial frequency metrology error and differences in mirror bonding considerations between the finite-element analysis model and the as-built mirror mount.
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.
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