Abstract

We describe results from the first multi-laser wavefront sensing system designed to support tomographic modes of adaptive optics (AO). The system, now operating at the 6.5 m MMT telescope in Arizona, creates five beacons by Rayleigh scattering of laser beams at 532 nm integrated over a range from 20 to 29 km by dynamic refocus of the telescope optics. The return light is analyzed by a Shack-Hartmann sensor that places all five beacons on a single detector, with electronic shuttering to implement the beacon range gate. A separate high-order Shack-Hartmann sensor records simultaneous measurements of wavefronts from a natural star. From open-loop measurements, we find the average beacon wavefront gives a good estimate of ground layer aberration. We present results of full tomographic wavefront analysis, enabled by supplementing the laser data with simultaneous fast image motion measurements from three stars in the field. We describe plans for an early demonstration at the MMT of closed-loop ground layer AO, and later tomographic AO.

© 2006 Optical Society of America

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  1. G. A. Tyler, "Merging: a new method for tomography through random media," J. Opt. Soc. Am. A 11,409-424 (1994).
    [CrossRef]
  2. M. Johns, J. R. P. Angel, S. Shectman, R. Bernstein, D. Fabricant, P. McCarthy, and M. Phillips, "Status of the Giant Magellan Telescope (GMT) project," in Ground-Based Telescopes, J. M. Oschmann, ed., Proc. SPIE 5489, 441-453 (2004).
    [CrossRef]
  3. L. M. Stepp and S. E. Strom, "The Thirty-Meter Telescope project design and development phase," in Second Bäckaskog Workshop on Extremely Large Telescopes, A. L. Ardeberg and T. Andersen, eds., Proc. SPIE 5382, 67-75 (2004).
    [CrossRef]
  4. P. L. Wizinowich et al., "The W. M. Keck Observatory laser guide star adaptive optics system: overview," Publ. Astron. Soc. Pac. 118, 297-309 (2006).
    [CrossRef]
  5. A. Tracy, A. Hankla, C. Lopez, D. Sadighi, K. Groff, C. d’Orgeville, M. Sheehan, D. Bamford, S. Sharpe, and D. Cook, "High-power solid-state sodium guidestar laser for the Gemini North Observatory," in Solid State Lasers XV: Technology and Devices, H. J. Hoffman and R. K. Shori, eds., Proc. SPIE 6100, 404-415 (2006).
  6. H. Takami et al. "Laser guide star AO project at the Subaru Telescope," in Advancements in Adaptive Optics, D. Bonaccini, B. L. Ellerbroek, and R. Ragazzoni, eds., Proc. SPIE 5490, 837-845 (2004).
    [CrossRef]
  7. M. Kasper, J. Charton, B. Delabre, R. Donaldson, E. Fedrigo, G. Hess, N. Hubin, J.-L. Lizon, M. Nylund, C. Soenke, and G. Zins, "LGS implementation for NAOS," in Advancements in Adaptive Optics, D. Bonaccini, B. L. Ellerbroek, and R. Ragazzoni, eds., Proc. SPIE 5490, 1071-1078 (2004).
    [CrossRef]
  8. R. Ragazzoni, E. Marchetti, and G. Valente, "Adaptive-optics corrections available for the whole sky," Nature 403,54-56 (2000).
    [CrossRef] [PubMed]
  9. M. Langlois, T. Rimmele, and G. Moretto, "Solar multiconjugate adaptive optics at the Dunn Solar Telescope: preliminary results," in Advancements in Adaptive Optics, D. Bonaccini, B. L. Ellerbroek, and R. Ragazzoni, eds., Proc. SPIE 5490, 59-66 (2004).
    [CrossRef]
  10. T. Berkefeld, D. Soltau, and O. von der Lühe, "Second-generation adaptive optics for the 1.5 m solar telescope GREGOR, Tenerife," in Advancements in Adaptive Optics, D. Bonaccini, B. L. Ellerbroek, and R. Ragazzoni, eds., Proc. SPIE 5490, 260-267 (2004).
    [CrossRef]
  11. F. Rigaut, "Ground-conjugate wide field adaptive optics for the ELTs," in Beyond Conventional Adaptive Optics, E. Vernet, R. Ragazzoni, S. Esposito, and N. Hubin, eds., Vol. 58 of ESO Proceedings Series, (European Southern Observatory, Garching, 2002), pp. 11-16.
  12. A. Tokovinin, "Ground layer sensing and compensation," in Second Bäckaskog Workshop on Extremely Large Telescopes, A. L. Ardeberg and T. Andersen, eds., Proc. SPIE 5382, 490-499 (2004).
    [CrossRef]
  13. A. Tokovinin, "Seeing improvement with ground-layer adaptive optics," Publ. Astron. Soc. Pac. 116,941-951 (2004).
    [CrossRef]
  14. D. R. Anderson, NRC Herzberg Institute of Astrophysics, 5071 W. Saanich Road, Victoria, BC V9E 2E7, et al., are preparing a manuscript to be called "Modelling a ground layer adaptive optics system".
  15. M. Lloyd-Hart, C. Baranec, N. M. Milton, T. Stalcup, M. Snyder, N. Putnam, and J. R. P. Angel, "First tests of wavefront sensing with a constellation of laser guide beacons," Astrophys. J. 634,679-686 (2005).
    [CrossRef]
  16. T. E. Stalcup, J. A. Georges, M. Snyder, C. Baranec, N. Putnam, N. M. Milton, J. R. P. Angel, and M. Lloyd-Hart, "Field tests of wavefront sensing with multiple Rayleigh laser guide stars and dynamic refocus," in Advancements in Adaptive Optics, D. Bonaccini, B. L. Ellerbroek, and R. Ragazzoni, eds., Proc. SPIE 5490, 1021-1032 (2004).
    [CrossRef]
  17. R. Q. Fugate, "The Starfire Optical Range 3.5-m adaptive optical telescope," in Large Ground-Based Telescopes, J. M. Oschmann and L. M. Stepp, eds., Proc. SPIE 4837, 934-943 (2003).
    [CrossRef]
  18. D. T. Gavel, S. S. Olivier, B. J. Bauman, C. E. Max, and B. A. Macintosh, "Progress with the Lick adaptive optics system," in Adaptive Optical Systems Technology, P. L. Wizinowich, ed., Proc. SPIE 4007, 63-70 (2000).
    [CrossRef]
  19. R. Q. Fugate, L. M. Wopat, D. L. Fried, G. A. Ameer, S. L. Browne, P. H. Roberts, G. A. Tyler, B. R. Boeke, and R. E. Ruane, "Measurement of atmospheric wavefront distortion using scattered light from a laser guide-star," Nature 353,141-146 (1991).
    [CrossRef]
  20. J. A. Georges, P. Mallik, T. Stalcup, J. R. P. Angel, and R. Sarlot "Design and testing of a dynamic refocus system for Rayleigh laser beacons," in Adaptive Optical System Technologies II, P. L.Wizinowich and D. Bonaccini, eds., Proc. SPIE 4839, 473-483 (2002).
    [CrossRef]
  21. J. Verin, A. Agabi, R. Avila, M. Azouit, R. Conan, F. Martin, E. Masciadri, L. Sanchez, and A. Ziad, "Gemini site testing campaign. Cerro Pachon and Cerro Tololo," Gemini RPT-AO-G0094, http://www.gemini.edu/ (2000).
  22. J. W. Hardy, Adaptive Optics for Astronomical Telescopes, (OUP, New York, 1998), Chap. 3.
  23. M. Lloyd-Hart and N. M. Milton, "Fundamental limits on isoplanatic correction with multiconjugate adaptive optics," J. Opt. Soc. Am. A 20,1949-1957 (2003).
    [CrossRef]
  24. F. Chassat, Propagation optique à travers la turbulence atmosphérique. Etude modale de l’anisoplanétisme et application à l’optique adaptative, PhD thesis, Université Paris-Sud (1992).
  25. T. Fusco et al., "NAOS performance characterization and turbulence parameters estimation using closed-loop data," in Advancements in Adaptive Optics, D. Bonaccini, B. L. Ellerbroek, and R. Ragazzoni, eds., Proc. SPIE 5490, 118-129 (2004).
    [CrossRef]
  26. B. Le Roux, J.-M. Conan, C. Kulcsár, H.-F. Reynaud, L. M. Mugnier, and T. Fusco, "Optimal control law for classical and multiconjugate adaptive optics," J. Opt. Soc. Am. A 21,1261-1276 (2004).
    [CrossRef]
  27. R.W. Wilson, "SLODAR: measuring optical turbulence altitude with a Shack-Hartmann wavefront sensor," Mon. Not. R. Astron. Soc. 337,103-108 (2002).
    [CrossRef]

2006

P. L. Wizinowich et al., "The W. M. Keck Observatory laser guide star adaptive optics system: overview," Publ. Astron. Soc. Pac. 118, 297-309 (2006).
[CrossRef]

2005

M. Lloyd-Hart, C. Baranec, N. M. Milton, T. Stalcup, M. Snyder, N. Putnam, and J. R. P. Angel, "First tests of wavefront sensing with a constellation of laser guide beacons," Astrophys. J. 634,679-686 (2005).
[CrossRef]

2004

2003

2002

R.W. Wilson, "SLODAR: measuring optical turbulence altitude with a Shack-Hartmann wavefront sensor," Mon. Not. R. Astron. Soc. 337,103-108 (2002).
[CrossRef]

2000

R. Ragazzoni, E. Marchetti, and G. Valente, "Adaptive-optics corrections available for the whole sky," Nature 403,54-56 (2000).
[CrossRef] [PubMed]

1994

1991

R. Q. Fugate, L. M. Wopat, D. L. Fried, G. A. Ameer, S. L. Browne, P. H. Roberts, G. A. Tyler, B. R. Boeke, and R. E. Ruane, "Measurement of atmospheric wavefront distortion using scattered light from a laser guide-star," Nature 353,141-146 (1991).
[CrossRef]

Ameer, G. A.

R. Q. Fugate, L. M. Wopat, D. L. Fried, G. A. Ameer, S. L. Browne, P. H. Roberts, G. A. Tyler, B. R. Boeke, and R. E. Ruane, "Measurement of atmospheric wavefront distortion using scattered light from a laser guide-star," Nature 353,141-146 (1991).
[CrossRef]

Angel, J. R. P.

M. Lloyd-Hart, C. Baranec, N. M. Milton, T. Stalcup, M. Snyder, N. Putnam, and J. R. P. Angel, "First tests of wavefront sensing with a constellation of laser guide beacons," Astrophys. J. 634,679-686 (2005).
[CrossRef]

Baranec, C.

M. Lloyd-Hart, C. Baranec, N. M. Milton, T. Stalcup, M. Snyder, N. Putnam, and J. R. P. Angel, "First tests of wavefront sensing with a constellation of laser guide beacons," Astrophys. J. 634,679-686 (2005).
[CrossRef]

Boeke, B. R.

R. Q. Fugate, L. M. Wopat, D. L. Fried, G. A. Ameer, S. L. Browne, P. H. Roberts, G. A. Tyler, B. R. Boeke, and R. E. Ruane, "Measurement of atmospheric wavefront distortion using scattered light from a laser guide-star," Nature 353,141-146 (1991).
[CrossRef]

Browne, S. L.

R. Q. Fugate, L. M. Wopat, D. L. Fried, G. A. Ameer, S. L. Browne, P. H. Roberts, G. A. Tyler, B. R. Boeke, and R. E. Ruane, "Measurement of atmospheric wavefront distortion using scattered light from a laser guide-star," Nature 353,141-146 (1991).
[CrossRef]

Conan, J.-M.

Fried, D. L.

R. Q. Fugate, L. M. Wopat, D. L. Fried, G. A. Ameer, S. L. Browne, P. H. Roberts, G. A. Tyler, B. R. Boeke, and R. E. Ruane, "Measurement of atmospheric wavefront distortion using scattered light from a laser guide-star," Nature 353,141-146 (1991).
[CrossRef]

Fugate, R. Q.

R. Q. Fugate, L. M. Wopat, D. L. Fried, G. A. Ameer, S. L. Browne, P. H. Roberts, G. A. Tyler, B. R. Boeke, and R. E. Ruane, "Measurement of atmospheric wavefront distortion using scattered light from a laser guide-star," Nature 353,141-146 (1991).
[CrossRef]

Fusco, T.

Kulcsár, C.

Le Roux, B.

Lloyd-Hart, M.

M. Lloyd-Hart, C. Baranec, N. M. Milton, T. Stalcup, M. Snyder, N. Putnam, and J. R. P. Angel, "First tests of wavefront sensing with a constellation of laser guide beacons," Astrophys. J. 634,679-686 (2005).
[CrossRef]

M. Lloyd-Hart and N. M. Milton, "Fundamental limits on isoplanatic correction with multiconjugate adaptive optics," J. Opt. Soc. Am. A 20,1949-1957 (2003).
[CrossRef]

Marchetti, E.

R. Ragazzoni, E. Marchetti, and G. Valente, "Adaptive-optics corrections available for the whole sky," Nature 403,54-56 (2000).
[CrossRef] [PubMed]

Milton, N. M.

M. Lloyd-Hart, C. Baranec, N. M. Milton, T. Stalcup, M. Snyder, N. Putnam, and J. R. P. Angel, "First tests of wavefront sensing with a constellation of laser guide beacons," Astrophys. J. 634,679-686 (2005).
[CrossRef]

M. Lloyd-Hart and N. M. Milton, "Fundamental limits on isoplanatic correction with multiconjugate adaptive optics," J. Opt. Soc. Am. A 20,1949-1957 (2003).
[CrossRef]

Mugnier, L. M.

Putnam, N.

M. Lloyd-Hart, C. Baranec, N. M. Milton, T. Stalcup, M. Snyder, N. Putnam, and J. R. P. Angel, "First tests of wavefront sensing with a constellation of laser guide beacons," Astrophys. J. 634,679-686 (2005).
[CrossRef]

Ragazzoni, R.

R. Ragazzoni, E. Marchetti, and G. Valente, "Adaptive-optics corrections available for the whole sky," Nature 403,54-56 (2000).
[CrossRef] [PubMed]

Reynaud, H.-F.

Roberts, P. H.

R. Q. Fugate, L. M. Wopat, D. L. Fried, G. A. Ameer, S. L. Browne, P. H. Roberts, G. A. Tyler, B. R. Boeke, and R. E. Ruane, "Measurement of atmospheric wavefront distortion using scattered light from a laser guide-star," Nature 353,141-146 (1991).
[CrossRef]

Ruane, R. E.

R. Q. Fugate, L. M. Wopat, D. L. Fried, G. A. Ameer, S. L. Browne, P. H. Roberts, G. A. Tyler, B. R. Boeke, and R. E. Ruane, "Measurement of atmospheric wavefront distortion using scattered light from a laser guide-star," Nature 353,141-146 (1991).
[CrossRef]

Snyder, M.

M. Lloyd-Hart, C. Baranec, N. M. Milton, T. Stalcup, M. Snyder, N. Putnam, and J. R. P. Angel, "First tests of wavefront sensing with a constellation of laser guide beacons," Astrophys. J. 634,679-686 (2005).
[CrossRef]

Stalcup, T.

M. Lloyd-Hart, C. Baranec, N. M. Milton, T. Stalcup, M. Snyder, N. Putnam, and J. R. P. Angel, "First tests of wavefront sensing with a constellation of laser guide beacons," Astrophys. J. 634,679-686 (2005).
[CrossRef]

Tokovinin, A.

A. Tokovinin, "Seeing improvement with ground-layer adaptive optics," Publ. Astron. Soc. Pac. 116,941-951 (2004).
[CrossRef]

Tyler, G. A.

G. A. Tyler, "Merging: a new method for tomography through random media," J. Opt. Soc. Am. A 11,409-424 (1994).
[CrossRef]

R. Q. Fugate, L. M. Wopat, D. L. Fried, G. A. Ameer, S. L. Browne, P. H. Roberts, G. A. Tyler, B. R. Boeke, and R. E. Ruane, "Measurement of atmospheric wavefront distortion using scattered light from a laser guide-star," Nature 353,141-146 (1991).
[CrossRef]

Valente, G.

R. Ragazzoni, E. Marchetti, and G. Valente, "Adaptive-optics corrections available for the whole sky," Nature 403,54-56 (2000).
[CrossRef] [PubMed]

Wilson, R.W.

R.W. Wilson, "SLODAR: measuring optical turbulence altitude with a Shack-Hartmann wavefront sensor," Mon. Not. R. Astron. Soc. 337,103-108 (2002).
[CrossRef]

Wizinowich, P. L.

P. L. Wizinowich et al., "The W. M. Keck Observatory laser guide star adaptive optics system: overview," Publ. Astron. Soc. Pac. 118, 297-309 (2006).
[CrossRef]

Wopat, L. M.

R. Q. Fugate, L. M. Wopat, D. L. Fried, G. A. Ameer, S. L. Browne, P. H. Roberts, G. A. Tyler, B. R. Boeke, and R. E. Ruane, "Measurement of atmospheric wavefront distortion using scattered light from a laser guide-star," Nature 353,141-146 (1991).
[CrossRef]

Astrophys. J.

M. Lloyd-Hart, C. Baranec, N. M. Milton, T. Stalcup, M. Snyder, N. Putnam, and J. R. P. Angel, "First tests of wavefront sensing with a constellation of laser guide beacons," Astrophys. J. 634,679-686 (2005).
[CrossRef]

J. Opt. Soc. Am. A

Mon. Not. R. Astron. Soc.

R.W. Wilson, "SLODAR: measuring optical turbulence altitude with a Shack-Hartmann wavefront sensor," Mon. Not. R. Astron. Soc. 337,103-108 (2002).
[CrossRef]

Nature

R. Q. Fugate, L. M. Wopat, D. L. Fried, G. A. Ameer, S. L. Browne, P. H. Roberts, G. A. Tyler, B. R. Boeke, and R. E. Ruane, "Measurement of atmospheric wavefront distortion using scattered light from a laser guide-star," Nature 353,141-146 (1991).
[CrossRef]

R. Ragazzoni, E. Marchetti, and G. Valente, "Adaptive-optics corrections available for the whole sky," Nature 403,54-56 (2000).
[CrossRef] [PubMed]

Publ. Astron. Soc. Pac.

P. L. Wizinowich et al., "The W. M. Keck Observatory laser guide star adaptive optics system: overview," Publ. Astron. Soc. Pac. 118, 297-309 (2006).
[CrossRef]

A. Tokovinin, "Seeing improvement with ground-layer adaptive optics," Publ. Astron. Soc. Pac. 116,941-951 (2004).
[CrossRef]

Other

D. R. Anderson, NRC Herzberg Institute of Astrophysics, 5071 W. Saanich Road, Victoria, BC V9E 2E7, et al., are preparing a manuscript to be called "Modelling a ground layer adaptive optics system".

M. Johns, J. R. P. Angel, S. Shectman, R. Bernstein, D. Fabricant, P. McCarthy, and M. Phillips, "Status of the Giant Magellan Telescope (GMT) project," in Ground-Based Telescopes, J. M. Oschmann, ed., Proc. SPIE 5489, 441-453 (2004).
[CrossRef]

L. M. Stepp and S. E. Strom, "The Thirty-Meter Telescope project design and development phase," in Second Bäckaskog Workshop on Extremely Large Telescopes, A. L. Ardeberg and T. Andersen, eds., Proc. SPIE 5382, 67-75 (2004).
[CrossRef]

T. E. Stalcup, J. A. Georges, M. Snyder, C. Baranec, N. Putnam, N. M. Milton, J. R. P. Angel, and M. Lloyd-Hart, "Field tests of wavefront sensing with multiple Rayleigh laser guide stars and dynamic refocus," in Advancements in Adaptive Optics, D. Bonaccini, B. L. Ellerbroek, and R. Ragazzoni, eds., Proc. SPIE 5490, 1021-1032 (2004).
[CrossRef]

R. Q. Fugate, "The Starfire Optical Range 3.5-m adaptive optical telescope," in Large Ground-Based Telescopes, J. M. Oschmann and L. M. Stepp, eds., Proc. SPIE 4837, 934-943 (2003).
[CrossRef]

D. T. Gavel, S. S. Olivier, B. J. Bauman, C. E. Max, and B. A. Macintosh, "Progress with the Lick adaptive optics system," in Adaptive Optical Systems Technology, P. L. Wizinowich, ed., Proc. SPIE 4007, 63-70 (2000).
[CrossRef]

A. Tracy, A. Hankla, C. Lopez, D. Sadighi, K. Groff, C. d’Orgeville, M. Sheehan, D. Bamford, S. Sharpe, and D. Cook, "High-power solid-state sodium guidestar laser for the Gemini North Observatory," in Solid State Lasers XV: Technology and Devices, H. J. Hoffman and R. K. Shori, eds., Proc. SPIE 6100, 404-415 (2006).

H. Takami et al. "Laser guide star AO project at the Subaru Telescope," in Advancements in Adaptive Optics, D. Bonaccini, B. L. Ellerbroek, and R. Ragazzoni, eds., Proc. SPIE 5490, 837-845 (2004).
[CrossRef]

M. Kasper, J. Charton, B. Delabre, R. Donaldson, E. Fedrigo, G. Hess, N. Hubin, J.-L. Lizon, M. Nylund, C. Soenke, and G. Zins, "LGS implementation for NAOS," in Advancements in Adaptive Optics, D. Bonaccini, B. L. Ellerbroek, and R. Ragazzoni, eds., Proc. SPIE 5490, 1071-1078 (2004).
[CrossRef]

M. Langlois, T. Rimmele, and G. Moretto, "Solar multiconjugate adaptive optics at the Dunn Solar Telescope: preliminary results," in Advancements in Adaptive Optics, D. Bonaccini, B. L. Ellerbroek, and R. Ragazzoni, eds., Proc. SPIE 5490, 59-66 (2004).
[CrossRef]

T. Berkefeld, D. Soltau, and O. von der Lühe, "Second-generation adaptive optics for the 1.5 m solar telescope GREGOR, Tenerife," in Advancements in Adaptive Optics, D. Bonaccini, B. L. Ellerbroek, and R. Ragazzoni, eds., Proc. SPIE 5490, 260-267 (2004).
[CrossRef]

F. Rigaut, "Ground-conjugate wide field adaptive optics for the ELTs," in Beyond Conventional Adaptive Optics, E. Vernet, R. Ragazzoni, S. Esposito, and N. Hubin, eds., Vol. 58 of ESO Proceedings Series, (European Southern Observatory, Garching, 2002), pp. 11-16.

A. Tokovinin, "Ground layer sensing and compensation," in Second Bäckaskog Workshop on Extremely Large Telescopes, A. L. Ardeberg and T. Andersen, eds., Proc. SPIE 5382, 490-499 (2004).
[CrossRef]

J. A. Georges, P. Mallik, T. Stalcup, J. R. P. Angel, and R. Sarlot "Design and testing of a dynamic refocus system for Rayleigh laser beacons," in Adaptive Optical System Technologies II, P. L.Wizinowich and D. Bonaccini, eds., Proc. SPIE 4839, 473-483 (2002).
[CrossRef]

J. Verin, A. Agabi, R. Avila, M. Azouit, R. Conan, F. Martin, E. Masciadri, L. Sanchez, and A. Ziad, "Gemini site testing campaign. Cerro Pachon and Cerro Tololo," Gemini RPT-AO-G0094, http://www.gemini.edu/ (2000).

J. W. Hardy, Adaptive Optics for Astronomical Telescopes, (OUP, New York, 1998), Chap. 3.

F. Chassat, Propagation optique à travers la turbulence atmosphérique. Etude modale de l’anisoplanétisme et application à l’optique adaptative, PhD thesis, Université Paris-Sud (1992).

T. Fusco et al., "NAOS performance characterization and turbulence parameters estimation using closed-loop data," in Advancements in Adaptive Optics, D. Bonaccini, B. L. Ellerbroek, and R. Ragazzoni, eds., Proc. SPIE 5490, 118-129 (2004).
[CrossRef]

Supplementary Material (3)

» Media 1: MOV (13730 KB)     
» Media 2: MOV (1841 KB)     
» Media 3: MOV (1069 KB)     

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Figures (7)

Fig. 1.
Fig. 1.

Sample data from the three real-time cameras and the corresponding reconstructed wavefronts. The movie (1.8 MB) shows on the top row, from left to right, continuous and simultaneous sequences of frames from the NGS Shack-Hartmann sensor, the wide field asterism camera, and the LGS Shack-Hartmann sensor. (The star images in the asterism have been magnified ×4 compared to their spacing.) The boxed star in the asterism is the same as used on the NGS sensor; the light is split between the two. The lower panels show the reconstructed NGS wavefront (left), the individual LGS wavefronts (right) and the NGS wavefront as estimated by tomography (center). [Media 1]

Fig. 2.
Fig. 2.

Wavefront correction of starlight on the basis of the average LGS signals. The dashed lines show the uncorrected error while the solid lines show the RMS residual wavefront phase after ground layer correction as a function of angular distance between the star and the geometric center of the LGS constellation. Tilt (global image motion) is excluded since it is not sensed by the lasers.

Fig. 3.
Fig. 3.

The processing sequence for laser tomography AO. Light from each beacon is recorded by a wavefront sensor (1), and the individual beacon wavefronts are reconstructed (2). The three-dimensional structure of the aberration is recovered by tomography (3). A spatial integration along the line of sight estimates the stellar aberration (4), which is mapped onto the DM actuators (5) and (in a closed-loop AO system) integrated in time to give the required actuator commands (6). In practice, steps (2) through (5) can be implemented as a single matrix-vector multiplication.

Fig. 4.
Fig. 4.

Sample frame from the asterism camera. Light from the central star was also fed to the NGS WFS. Image motion of the three brightest stars surrounding this one were used to estimate global tilt and second order modes in the tomographic reconstruction. The positions of the beacons are illustrated by the green stars. To account for field rotation, the LGS pattern was rotated in the beam projector optics, maintaining a fixed orientation with respect to the asterism as the MMT tracked.

Fig. 5.
Fig. 5.

Evolution of focus in the probe star’s wavefront, shown in blue on the two plots, with the ground layer estimate (a) and tomographic estimate (b) plotted in black.

Fig. 6.
Fig. 6.

For each of 9 data sets, each 60 s long, (a) shows the RMS wavefront error summed over orders 2–8 for the probe star wavefront without correction (blue squares), and with GLAO (red circles) and LTAO (green triangles) correction. Values of r 0, shown in (b) for a wavelength of 500 nm at zenith, have been computed for the total seeing (blue squares) and the ground layer contribution (red circles) only. The data sets were recorded over a 2 hour period and are here numbered chronologically.

Fig. 7.
Fig. 7.

Synthetic point-spread functions computed at 2.2 μm wavelength from wavefronts before and after correction. The movie (1 MB) shows PSFs with no correction (left), with GLAO correction (center), and with LTAO correction (right) over a 10 s period. The frame rate has been slowed from the original 50 Hz to 15 Hz. The lower panels show PSFs averaged over the full 60 s sequence.

Tables (1)

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Table 1. Image quality metrics at 1.25 μm, 1.65 μm and 2.2 μm.

Equations (2)

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a ̂ ps = Tb
T = A ps B .

Metrics