Adaptive secondary mirror demonstrator: design and simulation

Abstract

Atmospheric turbulence distorts the wavefront of the incoming light from an astronomical object and so limits the ability of a telescope to form perfect images. Adaptive optics is a combination of technologies that enable the correction of the wavefront distortion in real time. Conventional adaptive optics operate like auxiliary instruments and use additional relay optics, which reduce total throughput and introduce extra IR emissivity and polarization. Adaptive secondary mirrors avoid additional optical surfaces by providing the optical correction at an existing telescope surface (the secondary mirror). Previous studies have demonstrated the optical efficacy and mechanical feasibility of performing the adaptive correction in this way. A technique demonstrator is being developed to explore features and capabilities applicable to a large adaptive secondary mirror and to explore manufacturing, assembly/ disassembly, calibration, and measurement techniques. The paper describes the design of the demonstrator and its predicted performance. © 1999 Society of Photo-Optical Instrumentation Engineers. [S0091-3286(99) Subject terms: adaptive optics; deformable mirror; wavefront corrections; secondary mirror.Paper 990017

Why Adaptive Secondaries?

“…The previous papers (Lee, Walker, & Doel 1999a, 1999b reported that the demonstrator can Ðt near-perfect tip/tilt with some other lower other Zernike terms, which was predicted by simulation and proven by experiments. Figures 9 and 10 show the inÑuence functions of the central and outer actuators of the demonstrator and its ability to Ðt low-order Zernike terms.…”

First order analysis of thin plate deformable mirrors

“…From previous studies [2][3][4][5][6], for a mirror that was very stiff compared to the actuators, the influence functions were Gaussian which extended beyond the actuator by two to three times the actuator spacing. As the actuator stiffness was increased with respect to the mirror, the influence function became narrower, and less Gaussian in shape.…”

Adaptive secondary mirror demonstrator: construction and preliminary evaluation

“…The control signals were derived as described in Ref. 9. Because of nonlinearity ͑hysteresis and thermal expansion͒ of the prototype actuators and electrical noise in the displacement sensors, the actuator control signals required to match the Zernike terms were slightly different from those calculated using the measured influence functions.…”

“…1͒ was previously presented. 9 This paper describes the construction, assembly techniques and subsequent preliminary static and dynamic performance evaluation. As discussed in the next section, the key considerations in building an ASM are reliability and safety.…”

“…4͒. Currently, deformable secondary mirrors are being developed at the Steward Observatory in collaboration with ThermoTrex, 5 and at the Optical Science Laboratory [6][7][8][9][10] ͑OSL͒.…”