Deformable Mirror With Combined Piezoelectric And Electrostatic Actuators

Abstract

The light propagation through the atmosphere limits the high angular resolution in astronomical imaging. Active optics is a method to overcome this problem. It allows a real-time optimization of the resolving power. An active mirror was developed which consists of, an electrostatically deformable membrane with 5 cm in diameter. The 0.5 micron thick aluminized polymer foil is elongated by an electrode array with 63 hexagonal elements arranged in a ring structure. The sensitivity is in the region of 0,05 microns per volt. It works up to 4 kHz without resonances. The maximum local tilt of the membrane is 3 microns per 5 millimeter. For an atmospheric tilt compensation of the wavefront the mirror housing is in a gimbal-mount. Piezo-electric actuators provide a total mirror angular movement up to 20 Hz and angular sensitivity of 77 arcsecs per kV. With this active mirror device and a multiprocessor-microprocessor control unit the stabilisation of the star-speckle pattern positions and the deconvolution of the speckle patterns are possible. Two control methods are in development and analized in comparison. One of them is working with a modified shearing interferometer as a wave-front sensor and a feedback with cross-talk compensation. The other is sensing the optical information in the image plane by a diode-array and estimating the wave-front by trial and error or different more sophisticated algorithms. The previous system is designed for the 0,75 m RC-telescope with alt-az mount at the Landessternwarte in Heidelberg, FRG.© (1982) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.