Performance evaluation of the SAAO adaptive optics system

Abstract

This paper describes laboratory evaluations ofthe SAAO Adaptive Optics (AO) System, which is installed at the Air Force AEOS facility at Haleakala on the island ofMaui in Hawaii. The AO system includes a 32x32-channel wavefront sensor, a high-speed wavefront reconstructor, a 94 1-actuator deformable mirror, a high-bandwidth steering mirror, and a tracking sensor for tilt control. The performance metrics discussed include track bandwidth, trackjitter vs. target brightness, AO system temporal response, and the resulting Strehl ratios and MTF for a range oftarget brightnesses. Test methods and results are described.The SAAO adaptive optics system underwent acceptance testing at the Raytheon factory in Danbury, Connecticut, in February and March of 1999. A full description ofthe system can be found in the paper "The SAAO Adaptive Optics System," included in this proceedings. This paper briefly describes the testing and the measured performance ofthe SAAO adaptive optics system. Mission analysis performed by the Air Force team responsible for the procurement ofthe AEOS facility set the requirements for imaging performance. These requirements took the form of a set of MTF curves. The curves were generated from detailed system models, using as inputs the basic parameters ofthe main telescope, and a statistical representation ofthe expected atmospheric disturbance prevailing at the site. The disturbances were a Fried "coherence length" rO of 5 centimeters evaluated at 750 nanometers, and a Greenwood frequency2 of 122 Hz, with a 45 degree elevation angle measured from the zenith.The production ofphase disturbance optics (phase plates,) to be used as a physical test input disturbance, and that would faithfully represent the statistical parameters ofatmospheric disturbance stated above, was abandoned early in the program as a cost-saving measure. It was decided that performance assessment would be obtained by heavy reliance on a full-up system model (proprietary to Raytheon,) the behavior of which would be anchored to the hardware. (A description ofthis model is included in the paper "Modeling ofthe SAAO Adaptive Optics System," also included in this proceedings.) The closed-loop behavior of the model was to be tied to the actual hardware by means ofmeasuring bandwidths and phase margins of the actual hardware under certain conditions, using an on-board test light source (the OSS; see "The SAAO Adaptive Optics System" in this proceedings for a description) and applying the measured values to the In Gas, Chemical, and Electrical Lasers and Intense Beam Control and Applications, Santanu Basu,

An Analysis of Fundamental Waffle Mode in Early AEOS Adaptive Optics Images

“…We do not account for pointing variations or pupil wander in the telescope beam, nor do we employ a realistic model of the DM. Abreu et al (2000) noted that pinned and slaved actuators may provide as much as a 10% hit to the observed Strehl, while actuator influence functions and actuator dynamics will also limit the quality of the wave-front reconstruction. Any observed noncommon path aberrations between the AEOS WFS/DM and the VisIm will also degrade the observed Strehl ratios, as will the effects of the VisIm detector pixel modulation transfer function (MTF).…”

“…In fact, the presence of immobile DM actuators in the AEOS pupil imprints a phase and an amplitude error across the entire pupil. Abreu et al (2000) has estimated the Strehl hit to AEOS AO system performance due to these immobile actuators at ∼10%. Initial work has suggested these failed actuators can mimic localized waffle modes described by Gavel (2003).…”

Characterization of the AEOS Adaptive Optics System

“…The AO system and the Visible Imager (VisIm) camera were built by BF Goodrich of Danbury, Connecticut (formerly Raytheon Optical Systems), under contract to the US Air Force Research Laboratory's Directed Energy Directorate (AFRL/ DE; Abreu et al 2000aAbreu et al , 2000bGullapalli et al 2000). In the following subsections, we describe the main functional components of the AO system.…”

Faint companion search to O-stars using the adaptive optics system on the 3.63-meter telescope on Haleakala

“…[2][3][4][5] In short, the telescope (an altitude-azimuth design) uses a standard 7 mirror configuration (the optical axis between mirrors 3 and 4 is along the altitude mechanical axis; the optical axis between mirrors 6 and 7 is along the azimuth mechanical axis) to convey light to the AO system located several floors below the telescope. The AO system can send the compensated beam to one of seven experiment rooms.…”