Abstract

An experimental optical bench test-bed for developing new wavefront sensing concepts for Multi-Conjugate Adaptive Optics (MCAO) systems is described. The main objective is to resolve imaging problems associated with wavefront sensing of the atmospheric turbulence for future MCAO systems on Extremely Large Telescopes (ELTs). The test-bed incorporates five reference sources, two deformable mirrors (DMs) and atmospheric phase screens to simulate a scaled version of a 10-m adaptive telescope operating at the K band. A recently proposed compact tomographic wavefront sensor is employed for star-oriented DMs control in the MCAO system. The MCAO test-bed is used to verify the feasibility of the wavefront sensing concept utilizing a field lenslet array for multi-pupil imaging on a single detector. First experimental results of MCAO correction with the proposed tomographic wavefront sensor are presented and compared to the theoretical prediction based on the characteristics of the phase screens, actuator density of the DMs and the guide star configuration.

© 2005 Optical Society of America

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References

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ESO sym. on Lrg Telescopes & Their Instr

J. M. Beckers, �??Increasing the size of the isoplanatic patch with multiconjugate adaptive optics,�?? in ESO symposium on Large Telescopes and Their Instrumentation (European Southern Observatory, Garching, Germany, 1988), 693-703.

JOSA

R. J. Noll, �??Zernike polynomials and atmospheric turbulence�?? JOSA 66, 207-211 (1976).
[CrossRef]

JOSA A

B. L. Ellerbroek, �??Linear system modeling of adaptive optics in the spatial-frequency domain�??, JOSA A 22, 310-322 (2005).
[CrossRef] [PubMed]

D.M. Winker, �??Effect of a finite outer scale on the Zernike decomposition of atmospheric optical turbulence�??, JOSA A 8, 1568-1573 (1991).
[CrossRef]

J. Stone, P.H. Hu, S.P. Mills, and S. Ma, �??Anisoplanatic effects in finite-aperture optical systems,�?? JOSA A 11, 347-357 (1994).
[CrossRef]

M. Owner-Petersen and A. Goncharov, �??Multiconjugate adaptive optics for large telescopes: analytical control of the mirror shapes,�?? JOSA A 19, 537-548 (2002).
[CrossRef] [PubMed]

Opt. Eng.

A. Goncharov, M. Owner-Petersen, T. Andersen, and J. Beckers, �??Adaptive optics schemes for future extremely large telescopes,�?? Opt. Eng. 41, 1065-1072 (2002).
[CrossRef]

Opt. Express

Opt. Lett.

A.V. Goncharov, S. Esposito and J. C. Dainty, �??Multi-directional wavefront sensing for MCAO�??, Opt. Lett., (accepted for publication).
[PubMed]

Proc SPIE

R. Ragazzoni, J. Farinato and E. Marchetti, �??Adaptive Optics for 100m-class telescope: new challenges required new solutions,�?? in Adaptive optical system technology, P.L. Wizinovich, ed., Proc. SPIE 4007, 1076-1087 (2000).

P. Diericks, E. Brunetto, F. Comeron, R. Gilmozzi, F. Gonte, F. Koch, M. le Louarn, G. Monnet, J. Spyromilio, I. Surdej, C. Verinaud and N. Yaitskova, �??OWL Phase a Status Report�?? in Ground-based Telescopes, J. M. Oschmann ed., Proc. SPIE 5489, 391-406 (2004).

A. Goncharov, �??Optical Design for Advanced Extremely Large Telescopes,�?? in Ground-based Telescopes, J. M. Oschmann ed., Proc. SPIE 5489, 518-525 (2004).

E. Pinna, A. T. Puglisi, S. Esposito, A. Tozzi and A. V. Goncharov, �??Simple implementation of phase screens for repeatable seeing generation,�?? in Advancements in Adaptive Optic, D. Bonaccini Calia, B. Ellerbroek and R. Ragazzoni eds., Proc. SPIE 5490, 830-836 (2004).

J. Kolb, E. Marchetti, S. Tisserand, F. Franza, B. Delabre, F. Gonte, R. Brast, S. Jacob and F. Reversat, �??MAPS: a turbulence simulator for MCAO,�?? Simple in Advancements in Adaptive Optic, D. Bonaccini Calia, B. Ellerbroek and R. Ragazzoni eds., Proc. SPIE 5490, 794-804 (2004).

Proc. SPIE

R. Dekany, M. Britton, D. Gavel, B. Ellerbroek, G. Herriot, C. Max, and J.-P. Veran, �??Adaptive Optics Requirements Definition for TMT,�?? in Advancements in Adaptive Optics, D. Bonaccini Calia, B. Ellerbroek and R. Ragazzoni eds., Proc. SPIE 5490, 879-890 (2004).

Other

T. Andersen, A. Ardeberg and M. Owner-Petersen, Euro50. Design Study of a 50 m Adaptive Optics Telescope, (Lund Observatory, 2003).

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Figures (10)

Fig. 1.
Fig. 1.

Optical layout of the tomographic wavefront sensor: 1 – the telescope entrance pupil; 2 – telescope objective, 3 – field lenslet array; 4 – collimator; 5 – Shack-Hartmann lenslet array; 6 – SH focal plane; 7 – field flattener lens; 8 – reimaging two-doublet system; 9 – CCD camera imaging plane.

Fig. 2.
Fig. 2.

Magnified optical layout: pupil separation in the tomographic WFS (left side), rays pass near the CCD plane (right side), for legend see Fig. 1 caption.

Fig. 3.
Fig. 3.

Optical layout and actual arrangement of the MCAO test-bed.

Fig. 4.
Fig. 4.

Optical layout of NGSs and atmospheric turbulence module: 1 – guide star plane; 2 – first collimator; 3 – first beam splitter; 4 – afocal system; 5 – high altitude layer DM2; 6 – second beam splitter; 7 – ground layer DM1 (telescope pupil); 8 – collimated light entering tomographic WFS; PS1 and PS2 are the phase screens.

Fig. 5.
Fig. 5.

Full Field Spot Diagrams: (a) metapupil on DM2 (10 km conjugation), (b) Hartmann spots on the CCD (Zemax simulation), and (c) real Hartmann spots in selected boxes on the CCD.

Fig. 6.
Fig. 6.

Target star and location of the phase screen during the static aberration correction in dual-conjugate AO: star field with a target under the test, (b) two locations of the turbulent layer, and (c) phase screen.

Fig. 7.
Fig. 7.

Target star image: original image in the focal plane (left side); Zemax Polycromatic diffraction point spread function normalize to the peak intensity of the unaberrated image (right side), box size is 360 µm.

Fig. 8.
Fig. 8.

Phase maps for the intersection region of the five probing beams with the phase screen at 30 km height.

Fig. 9.
Fig. 9.

Upper layer static aberration correction for conjugations: PS2=20km, OKO37=0 km, OKO59=10 km.

Fig. 10.
Fig. 10.

Low layer static aberration correction for conjugations: PS1=-5km, OKO37=0 km, OKO59=10 km

Tables (2)

Tables Icon

Table 1. Essential parameters for the optical components in the MCAO test-bed system.

Tables Icon

Table 2. Experimental results for five-star AO correction measured on the target star.

Equations (2)

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A = U Σ V T ,
C = A 1 * = V Σ 1 * U T

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