Applications of Smart Sturctures for Deformable Mirrors
- Paper number
IAC-20,C2,9,1,x56886
- Author
Dr. Brij Agrawal, United States, Naval Postgraduate School
- Year
2020
- Abstract
Smart actuators such as lead zicronate titanate (PZT) and lead magnesium niobate (PMN) are commonly used to actively deform surfaces of optical mirrors in many applications. These actuators can be used either normal or parallel to the mirror surface. Deformable mirrors are used in adaptive optics for correcting aberration in optical beam due to atmospheric turbulence and in space telescopes to correct primary mirror manufacturing and environmental surface errors. For these applications, mirror surface must be deformed with very fine accuracy in the range of nano meters. Adaptive Optics Center of Excellence (AOC) at the Naval Postgraduate School has been very active in research for the application of deformable mirrors for adaptive optics and space telescopes. This paper will present the results of this research with emphasis on different designs of deformable mirrors. Depending on the application, deformable mirrors are selected for actuator material, PZT or PMN, mirror diameter, number of actuators, actuator pitch, and actuator mechanical stroke. AOC has deformable mirrors both with PZT and PMN actuators and diameters from 30 to 100 mm, number of actuators from 10 to 349, pitch from 2.5 to 6 mm, and stroke from 2.5 to 8 micrometers from several manufacturers. AOC also has segmented mirror telescope whose primary mirror has six 1-meter diameter segments for a 3-meter aperture. Each segment has 156 PMN actuators mounted parallel to the surface. Actuators are used to correct mirror surface manufacturing error and on-orbit surface distortion. There are certain advantages and disadvantages in using PZT vs PMN, actuators normal to surface vs parallel and tradeoffs of number of actuators, pitch, and stroke. PZT is non-poled ceramic whose longitudinal elongation is proportional to the applied voltage. PMN is a non-poled ceramic whose longitudinal elongation is proportional to the square of the applied voltage. PMN has lower hysteresis in comparison to PZT. Actuators normal to mirror surface give local distortion. Actuators parallel to mirror surface give global distortion. Integrated optical and optical structural model was also developed to predict mirror surface distortion and optical performance as a function of applied voltages to PMN actuators. This paper will cover these topics.
- Abstract document
- Manuscript document
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