Single Crystal Piezoelectric Actuators for Advanced Deformable Mirrors

In this paper, single crystal piezoelectric actuators are developed and demonstrated as a means of increasing actuator authority while maintaining strain precision for adaptive optics used large throw deformable mirror applications. Single crystal (PMN-PT crystal) stack actuators with foot print size of 5 mm × 5 mm and height varied from 16 mm to 21 mm have been designed, fabricated and tested. The actuation stroke larger than 50 μm is obtained under driving electric field of 15 KV/cm for single crystal stack actuators. In-plane actuation stroke is about 25 μm under 8KV/cm for single crystal plate actuators. The characterization results show that the single crystal piezoelectric actuators hold enhanced stroke and coupling coefficient (>0.83) under lower driving field comparing with PZT counterpart, while keep the nature of piezoelectric actuations with high precision, high resolution, fast response under high preload stress. The potential benefits of incorporating these actuators in a deformable mirror (DM) design were demonstrated by system modeling using the Integrated Optical Design Analysis Software (IODA) developed by SRS. The modeling shows that low order aberrations with peak to valley errors as large as 40 microns could be corrected to diffraction limited performance with a reasonable number of actuators and acceptable actuator forces and face sheet stresses. In the case of DM correction with 20 microns of 1^st-Order Astigmatism-X error (Peak to valley: 38.74 μm, RMS error: 8.13 μm), the corrected wavefront error was reduced to PV of 0.26 μm and RMS error of 0.024 μm, which suggest promise for large throw DM applications.