Integrated Laboratory Demonstrations of Multi-Object Adaptive Optics on a Simulated 10 Meter Telescope at Visible Wavelengths

Abstract

One important frontier for astronomical adaptive optics (AO) involves methods such as Multi-Object AO and Multi-Conjugate AO that have the potential to give a significantly larger field of view than conventional AO techniques. A second key emphasis over the next decade will be to push astronomical AO to visible wavelengths. We have conducted the first laboratory simulations of wide-field, laser guide star adaptive optics at visible wavelengths on a 10-meter-class telescope. These experiments, utilizing the UCO/Lick Observatory's Multi-Object / Laser Tomography Adaptive Optics (MOAO/LTAO) testbed, demonstrate new techniques in wavefront sensing and control that are crucial to future on-sky MOAO systems. We (1) test and confirm the feasibility of highly accurate atmospheric tomography with laser guide stars, (2) demonstrate key innovations allowing open-loop operation of Shack-Hartmann wavefront sensors (with errors of ∼ 30 nm) as will be needed for MOAO, and (3) build a complete error budget model describing system performance. The AO system maintains a performance of 32.4% Strehl on-axis, with 24.5% and 22.6% at 10. ′′ and 15. ′′ , respectively, at a science wavelength of 710 nm (R-band) over the equivalent of 0.8 seconds of simulation. The mean ensquared energy on-axis in a 50 milliarcsecond spaxel is 46%. The off-axis Strehls are obtained at radial separations 2-3 times the isoplanatic angle of the atmosphere at 710 nm. The MOAO-corrected field of view is ∼ 25 times larger in area than that limited by anisoplanatism at R-band. The error budget we assemble is composed almost entirely of terms verified through independent, empirical experiments, with minimal parameterization of theoretical models. We find that error terms arising from calibration inaccuracies and optical drift are comparable in magnitude to traditional terms like fitting error and tomographic error. This makes a strong case for implementing additional calibration facilities in future AO systems, including accelerometers on powered optics, 3D turbulators, telescope and LGS simulators, and external calibration ports for deformable mirrors. These laboratory demonstrations add strong credibility to the implementation of on-sky demonstrators of Laser Tomographic Adaptive Optics (LTAO) on 5-10 meter telescopes in the coming years.

Analysis of on-sky MOAO performance of CANARY using natural guide stars

“…A first on-sky testing of on-axis openloop command has been already reported (Andersen et al 2008) as well as first MOAO laboratory demonstrations (Ammons et al 2010;Vidal et al 2010a). The next step is to demonstrate on-sky the capability of the open loop tomography using a number of in-the-field GS, both laser and natural.…”

MOAO first on-sky demonstration with CANARY

“…Other side effects are noticeable, such as the difficulty of calibrating any optical relationship between the WFSs and DMs placed in different optical trains. A first on-sky testing of on-axis open-loop command has been reported (Andersen et al 2008) as well as first MOAO laboratory demonstrations (Ammons et al 2010;Vidal et al 2010a). …”

Tomography reconstruction using the Learn and Apply algorithm

“…Ammons et al [5] use the Spherical Waves algorithm in the MOAO case for a 10m telescope, Costille et al [6], Petit et al [7] uses the Kalman based approach in Multi-Conjugate Adaptive Optics (MCAO) scheme, but none of them have been demonstrated in a real on-sky instrument.…”