Gemini Preprint #87

Near-infrared AO coronograph design for giant telescopes

Brent Ellerbroek

Gemini Observatory, 670 N. A'ohoku Pl., Hilo, HI 96720

Richard Buchroeder

Optical Design Service, 8 Bella Vista Drive, Tucson, AZ 85745


We describe the adaptive optical (AO) requirements, optical design, and expected performance of a near-infrared AO coronagraph for a 30 meter class giant telescope. The optical design of the instrument consists of back-to-back finite conjugate relays, each containing a collimated space between a pair of toric mirrors. The first collimated space contains the atmospheric dispersion compensator and the AO components, which are a tip/tilt mirror, a MEMS deformable mirror, and a beamsplitter for the wavefront sensing path. An occulting disk or similar focal plane mask is located at the intermediate image between the two relays, and a Lyot stop is placed at the pupil plane in the second relay. The required AO order of correction for a Strehl ratio of 0.9 at a wavelength of 2.2 microns is about 150 by 150, and the required control bandwidth is 42 Hz. The limiting magnitude at this level of performance is estimated to be 10.4.

Keywords: Adaptive optics, giant telescopes, coronagraphs

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Last updated by Virginia Smith / / August 2, 2002