Starpoint Adaptive Optics

The ELECTRA Project

The University of Durham's Astronomical Instrumentation Group developed a major astronomical adaptive optics instrument in the mid-1990s – ELECTRA. The instrument operated at the "GHRIL" Nasmyth platform of the UK's 4.2m William Herschel Telescope on La Palma in the Canary Islands. The adaptive mirror was of the segmented variety, 76 square segments, each with three degrees of freedom (tip; tilt; piston).

ELECTRA was the first operational AO system to use strain-gauge feedback to compensate for the hysteresis present in the adaptive mirror's piezoelectric actuators.

The picture shows the ELECTRA controls system in the GHRIL lab at the WHT in July 1998, next to Andrew Zadrozny, who developed it. The electronic control system is packaged in four racks for easy shipping and installation. It sits in the GHRIL control room, next door to the optics lab. The four racks, running from top to bottom are:

Rack 1: The Real Time VME Crate, containing an embedded Sparc CPU, the real time processing TI 320C44 DSPs, A-D boards to read the strain gauges, and interfaces to the Mirror DAC Rack and Wave-Front Sensor camera.

Rack 2: The EPICS Mechanisms control stuff - The upper half contains the power stages for the stepper motors, dc motors, alignment light sources... etc...
The lower half is a VME crate with the EPICS processor, a stepper motor controller and some binary I/O.

Rack 3: The High Voltage power amplifiers for the segmented Adaptive Mirror; 228 channels of +/-210V amplifiers.

Rack 4: The DACs feeding the high voltage amplifiers, and the high voltage PSU.

Hidden from view in the rear of the crates are the Strain Gauge PSU and the tip-tilt mirror drive rack.

Development work on ELECTRA began in early 1995, the instrument was on the telescope in June 1997, and then again in July 1998, when the strain gauge system was successfully commissioned. The adaptive mirror and associated control hardware were then transferred over to the NAOMI project, a common-user adaptive optics facility for the William Herschel Telescope, and have been operating at the WHT as part of this system since July 2000.

The project spawned some very useful technologies, such as a very compact, high channel-count HV amplifier system to drive the adaptive mirror. This is now a mature design that's demonstrated a very high degree of reliability. The key technologies from this work have been licenced by Starpoint Adaptive Optics, and now form part of its product portfolio.

Reference:
First Atmospheric Compensation With a Linearised High Order
Adaptive Mirror — ELECTRA.
A. Zadrozny, M.P.J.L. Chang, D.F. Buscher, R.M. Myers, A.P. Doel,
C.N. Dunlop, R.M. Sharples & R.L. Arnold.
In 'Topical Meeting on Astronomy with Adaptive Optics'. Ed. D. Bonaccini.
ESO Conf. Workshop Proc. No.56, 459 – 468 (1999). Full paper (Postscript)

A full listing of Andrew Zadrozny's publications in the fields of adaptive optics and high resolution imaging is given here.