Laser Guide Stars

By detecting backscattered light from a laser beam fired upwards, computers and adaptive optics can compensate for the distorting effects of atmospheric turbulence on astronomical images.

Like the gasdynamic laser this invention is a product of top secret military research on the 'Star Wars' laser defense program to allow high power ground based lasers to traverse the atmosphere without distortion, bounce off orbiting mirrors and shoot down intercontinental ballistic missiles. With the cutbacks in SDI and the end of Cold War some of this research was recently declassified to the delight of astronomers disappointed with the poor performance of the then crippled Hubble Space Telescope.


Mechanical Description

There are many prototype laser guide star systems currently in operation or in the testing phase such as the Lick Observatory system. Most are based on correcting the incoming optical wavefront using a laser to probe the index of refraction variations of the atmosphere along the path. With this knowledge computers and high speed deformable or tiltable mirrors can be used to reverse these wavefront distortions.

Some rudimentary wavefront correction systems which don't require lasers are based on a mirror which can be tilted in real-time in response to to the wandering of the star image about a centroid. These minute deflections originate from the atmosphere acting like a giant prism which varies over time bending the wavefront as a whole. It is much more difficult for such passive systems to adequately correct for higher order aberrations which change the shape of the point spread function due to multiple inhomogenieties in the atmospheric index of refraction along the light path. Laser guide star systems can offer an elegant solution to this problem by actively rather than passively sensing these inhomogenieties.

Comment

It is almost a paradox that astronomers have so rapidly accepted laser corrected telescope optics : They are comfortable firing lasers upwards and into outer space yet they fail to acknowledge that natural laser radiation may be coming from the other direction, from the very objects they are observing!

REFERENCES

  1. LLNL Laser Guide Star Adaptive Optics Program (see press release)
  2. Photos of Lick Observatory atop Mt. Hamilton, east of San Jose, Ca - computer-driven membrane-thin mirror with 127 individual actuators that can adjust the mirror 50-100 times per second to counteract the effects of atmospheric turbulence
  3. Lukin, V.P. : Atmospheric Adaptive Optics
  4. Hugo Weichel, H. : 1990, Laser Beam Propagation in the Atmosphere
  5. Adaptive Optics Associates Inc.
  6. ADONIS, Observatoire de Paris
  7. ALFA, Max Plank Institutes
  8. Anglo-Australian Telescope
  9. Canada-France-Hawaii Telescope
  10. European Southern Observatory
  11. Gemini
  12. Hubble Space Telescope
  13. Imperial College
  14. Keck Observatory
  15. Los Alamos National Laboratory
  16. Mount Wilson Observatory
  17. National Solar Observatory
  18. Palomar Observatory
  19. Royal Greenwich Observatory
  20. Starfire Optical Range
  21. Steward Observatory
  22. Subaru
  23. University of Chicago
  24. University of Durham
  25. University of Hawaii
  26. University of Illinois
  27. William Herschel Telescope
  28. Xinetics Inc.
Description of some of these sites by Univ. of Hawaii, the CFHT site also has a good list.
The Adonis/Comeon AO project.
This on-going European project produced what was probably (let me know it you know differently) the first operational AO system outside of the American (and possibly Russian) military.
The Gemini 8m telescope project.
Amongst other goodies, this page contains a nice introduction to the effects of AO on telescope imaging performance.
The Steward Observatory with their Center for Astronomical Adaptive Optics (CAAO)
All sorts of interesting things going on here. Take a look at this newly refurbished page (Feb 1996).
The Starfire Optical Range (SOR)
One of the leading military AO programs, run by Phillips Labs at Kirtland Airforce base, New Mexico. These chaps are a particularly renown for their laser guide star work.
The Imperial College Optics Group
This page contains a good introduction to the theory of Shack-Hartmann sensors. They have a very interesting technique for converting most IR cameras into wavefront sensors, and a couple of video clips showing the system in action.
The Subaru AO team now has their own WWW.
The home page shows results from their prototype AO system used on a telescope. Work for the Subaru AO project is being carried out by the National Astronomical Observatory in conjunction with the Advanced Technology Center of CRL.
The AAT AO system .
A system being built by the School of Physics, Sydney University, for the Anglo Australian Telescope.
The UnISIS project..
UnISIS stands for University of Illinois Seeing Improvement System. In its initial configuration, UnISIS will consist of a single deformable mirror with 13x13 independent segments and an excimer laser capable of creating a Rayleigh laser guide star at a wavelength of 351nm at a height of 18 km above the telescope.
The Mount Wilson AO project.
The 100" telescope at Mt Wilson is now equipped with a working AO system.
The CFHT's Puao AOB.
The Puao Adaptive Optics Bonnet is a 19 degree of freedom Curvature AO system, designed as a flexible user instrument for the CFHT telescope. The system is named after a native Hawaiian Owl.
The University of Chicago ChAOS AO system.
The project has the ultimate goal of producing inexpensive high order laser guide-star AO systems.
The LLNL Laser Guide Star Adaptive Optics program.
This program aims to produce a fully featured high order laser guide star AO system. They are currently installing a system at Lick Observatory, and are developing a system for the 10m Keck telescope.
The European Southern Observatory Adaptive Optics Team.
A good introduction to the complexity of organizing adaptive optics as a user instrument at an observatory.
The ACE system on the Mount Wilson 60 inch telescope.
Swords to ploughshares.
The MARTINI project.
One of the pioneering efforts in civilian adaptive optics.
The Palomar Adaptive Optics System at JPL.
The Palomar AO system will be a high order natural/laser guide star system.
The RGO AO project.
The ELECTRA Nad MARTINI AO research project at the University of Durham (UK).
This is one of the oldest civilian AO projects.
The WHT AO project
This project aims to place a "user instrument" class AO system on the GHRIL of the WHT telescope in La Palma.
The MPIA ALFA project.
This is a very ambitious laser guide star system, which is fast approaching completion. This system will be a real testbed for laser guide star technology.

Other work relating to Adaptive Optics

Micro optical deformable mirror technology from Delft University NL .
Interesting work on producing high spatial resolution deformable mirrors using silicon processing technology.

Commercial AO sources

Here is are some companies who offer products related to adaptive optics.
Xinetics Inc. .
Xinetics Inc. is a company specializing in the fabrication of commercial deformable mirrors and their associated driver electronics. These mirrors use PMN electrostrictive actuators which generate 4 microns of stroke for 100V applied with hysteresis of <1%. In addition to deformable mirrors they also sell cofired multilayer actuators and Silicon Carbide optics.
Adaptive Optics Associates Inc. .
Adaptive Optics Associates Inc. (AOA) has been in the business of supplying AO components and systems to both Government, commercial, and academic customers for 20 years. AOA has provided the wavefront sensor systems for the Starfire Optical Range and is currently fabricating a complete Laser Guide Star AO system for the Max-Planck Institute for Astronomy in Heidelberg.

LLNL Laser Guide Star and Adaptive Optics Publications

General Theory Papers

  1. "Sodium Guide Star Adaptive Optics System for Astronomical Imaging in the Visible and Near-Infrared", D. T. Gavel, J. R. Morris, and R. G. Vernon, 1992, in Proc. Laser Guide Star Adaptive Optics Workshop (Air Force Phillips Lab., Albuquerque, NM) p. 619.
  2. "Resolution Limits for Ground-Based Astronomical Imaging using Adaptive Optics", S. S. Olivier, D. T. Gavel, C. E. Max, and J. M. Brase, 1992, in Proc. Laser Guide Star Adaptive Optics Workshop (Air Force Phillips Lab., Albuquerque, NM) p. 567.
  3. "Development of Laser Guide Stars and Adaptive Optics for Large Astronomical Telescopes", C. E. Max, K. Avicola, H. Bissinger, J. M. Brase, D. T. Gavel, H. Friedman, J. R. Morris, S. S. Olivier, D. Rapp, J. T. Salmon, and K. Waltjen, 1992, in "Progress in Telescope and Instrumentation Technologies", Proc. European Southern Observatory no. 42 (European Southern Observatory, Garching,) p. 443.
  4. "Resolution Limits for Ground-Based Astronomical Imaging using Adaptive Optics", S. S. Olivier, C. E. Max, D. T. Gavel, and J. M. Brase, 1992, in "Progress in Telescope and Instrumentation Technologies", Proc. European Southern Observatory no. 42 (European Southern Observatory, Garching,), p. 489.
  5. "Tip-Tilt Compensation: Resolution Limits for Ground Based Telescopes using Laser Guide Star Adaptive Optics", S. S. Olivier, C. E. Max, D. Gavel, and J. Brase, 1993, Astrophysical Journal 407, p. 428.
  6. "Laser Guide Star Adaptive Optics: Present and Future", S. S. Olivier and C. E. Max, 1993, in "Very High Angular Resolution Imaging", Proc. International Astronomical Union Symposium No. 158, p. 283.
  7. "Atmospheric Turbulence Compensation by Resonant Optical Backscattering from the Sodium Layer in the Upper Atmosphere", W. Happer, G. J. MacDonald, C. E. Max, and F. J. Dyson, 1994, J. Optical Society of America A 11, p. 263.
  8. "Tip-Tilt Compensation For Astronomical Imaging", S. S. Olivier and D. T. Gavel, 1994, J. Optical Society of America A 11, p. 368.
  9. "Systematic Design and Analysis of Laser guide Star Adaptive Optics Systems for Large Telescopes", D. T. Gavel, J. R. Morris, and R. G. Vernon, 1994, J. Optical Society of America A 11, p. 914.
  10. "Efficient Excitation of a Mesospheric Sodium Laser Guide Star by Intermediate-Duration Pulses", J. R. Morris, 1994, J. Optical Society of America A 11, p. 832.
  11. "Simulation and analysis of laser guide star adaptive optics systems for the 8- to 10-meter-class telescopes", D. T. Gavel and S. S. Olivier, 1994, Proc. SPIE 2201, p. 295.

LGS Feasibility Experiments at LLNL

  1. "Feasibility Experiment for Sodium-Layer Laser Guide Stars at the Lawrence Livermore National Laboratory", C. E. Max, K. Avicola, H. Bissinger, J. Brase, D. Gavel, H. Friedman, J. Morris, S. Olivier, J. T. Salmon, and K. Waltjen, 1992, in Proc. Laser Guide Star Adaptive Optics Workshop (Air Force Phillips Lab., Albuquerque, NM) p. 535.
  2. "System Design for High Power Sodium Beacon Laser", H. Friedman, J. Morris, and J. Horton, 1992, in Proc. Laser Guide Star Adaptive Optics Workshop (Air Force Phillips Lab., Albuquerque, NM) p. 639.
  3. "High Frame-Rate Large Field Wavefront Sensor", K. Avicola, J. T. Salmon, J. Brase, K. Waltjen, R. Presta, and K. S. Bach, 1992, in Proc. Laser Guide Star Adaptive Optics Workshop (Air Force Phillips Lab., Albuquerque, NM) p. 776.
  4. "Laser Guide Star Measurements at Lawrence Livermore National Laboratory", H. Freidman, et al., 1992, Proc. SPIE 1920, p. 52.
  5. "Design and Early Results of the Sodium-Layer Laser Guide Star Adaptive Optics Experiment at the Lawrence Livermore National Laboratory", D. T. Gavel, C. E. Max, K. Avicola, H. D. Bissinger, J. M. Brase, J. Duff, H. W. Friedman, J. R. Morris, S. S. Olivier, D. A. Rapp, J. T. Salmon, and K. E. Waltjen, 1993, Proc. ICO-16 Satellite Conference on Active and Adaptive Optics, p.
  6. "Sodium Layer Laser Guide Star Adaptive Optics Development at Lawrence Livermore National Laboratory: System Description and Experimental Results", K. Avicola, J. Brase, J. Morris, H. Bissinger, H. Friedman, D. Gavel, R. Kiefer, C. E. Max, S. Olivier, D. Rapp, T. Salmon, D. Smauley, and K. Waltjen, 1994, Proc. SPIE 2201, p. 326.
  7. "Design, Layout, and Early Results of a Feasibility Experiment for Sodium-Layer Laser Guide Star Adaptive Optics", C. E. Max, K. Avicola, J. M. Brase, H. W. Friedman, H. D. Bissinger, J. Duff, D. T. Gavel, J. A. Horton, R. Kiefer, J. R. Morris, S. S. Olivier, R. W. Presta, D. A. Rapp, J. T. Salmon, and K. E. Waltjen, 1994, J. Optical Society of America A 11, p. 813.
  8. "Sodium-Layer Laser Guide Star Experimental Results", K. Avicola, J. M. Brase, J. R. Morris, H. D. Bissinger, J. M. Duff, H. W. Friedman, D. T. Gavel, C. E. Max, S. S. Olivier, R. W. Presta, D. A. Rapp, J. T. Salmon, and K. E. Waltjen, 1994, J. Optical Society of America A 11, p. 825.
  9. "An Adaptive Optics Package Designed for Astronomical Use with a Laser Guide Star Tuned to an Absorption Line of Atomic Sodium", J. T. Salmon, K. Avicola, J. Brase, J. W. Bergum, H. W. Friedman, D. T. Gavel, C. E. Max S. D. Mostek, S. S. Olivier, R. W. Presta, R. J. Rinnert, C. W. Swift, K. E. Waltjen, C. L. Weinzapfel, J. N. Wong, 1994, Proc. SPIE 2201, p. 212.
  10. "Sodium-Layer Laser Guide Star Adaptive Optics Development at Lawrence Livermore National Laboratory and Lick Observatory", S. S. Olivier, C. E. Max, K. Avicola, J. M. Brase, H. W. Friedman, D. T. Gavel, J. R. Morris, J. T. Salmon, H. D. Bissinger, J. Duff, E. M. Johansson, B. Johnston, R. D. Kiefer, R. W. Presta, D. A. Rapp, D. A. Smauley, and K. E. Waltjen, 1994, Proc. Astronomical Society of the Pacific, Vol. 55, p. 82.

Lick AO and LGS Experiments

  1. "Performance of Adaptive Optics at Lick Observatory", S. S. Olivier, J. An, K. Avicola, H. D. Bissinger, J. M. Brase, H. W.. Friedman, D. T. Gavel, E. M. Johansson, C. E. Max, K. E. Waltjen, W. Fisher, and W. Bradford, 1994, Proc. SPIE 2201, p. 1110.
  2. "Adaptive Optics at Lick Observatory: System Architecture and Operations", J. M. Brase, J. An, K. Avicola, H. D. Bissinger, H. W. Friedman, D. T. Gavel, B. Johnston, C. E. Max, S. S. Olivier, R. Presta, D. A. Rapp, J. T. Salmon, K. E. Waltjen, and W. Fisher, 1994, Proc. SPIE 2201, p. 474.
  3. "Design of a Fieldable Laser System for a Sodium Laser Guide Star", H. Friedman, G. Erbert, T. Kuklo, T. Salmon, D. Smauley, G. Thompson, and N. Wong, 1994, Proc. SPIE 2201, p. 352.
  4. "Performance of Laser Guide Star Adaptive Optics at Lick Observatory", S. S. Olivier, J. An, K. Avicola, H. D. Bissinger, J. M. Brase, H. W. Friedman, D. T. Gavel, C. E. Max, J. T. Salmon, and K. E. Waltjen, 1995, Proc. SPIE 2534, p. 26.
  5. "Sodium Beacon Laser System for the Lick Observatory", H. W. Friedman, G. V. Erbert, T. C. Kuklo, J. G. Malik, J. T. Salmon, D. A. Smauley, G. R. Thompson, and N. J. Wong, 1995, Proc. SPIE 2534, p. 150
  6. "A Sodium Guide Star Laser System for the Lick Observatory 3 meter Telescope", H. W. Friedman, G. V. Erbert, D. T. Gavel, T. C. Kuklo, J. G. Malik, J. T. Salmon, D. A. Smauley, G. R. Thompson, 1996, Proc. European Southern Observatory, Conference No. 54, p. 207.
  7. "Initial Results from the Lick Observatory Laser Guide Star Adaptive Optics System", S. S. Olivier, J. An, K. Avicola, H. D. Bissinger, J. M. Brase, D. T. Gavel, B. Macintosh, C. E. Max, J. T. Salmon, and K. E. Waltjen, 1996, Proc. European Southern Observatory Conference No. 54, p. 75.
  8. "Significant Image Improvement from a Sodium-layer Laser Guide Star Adaptive Optics System at Lick Observatory", C. E. Max, S. S. Olivier, H. W. Friedman, J. An, K. Avicola, B. V. Beeman, H. D. Bissinger, J. M. Brase, G. V. Erbert, D. T. Gavel, K. Kanz, B. Macintosh, K. P. Neeb, and K. E. Waltjen, 1997, submitted to Science.

Design of Keck AO and LGS Systems

  1. "Issues in the Design and Optimization of Adaptive Optics and Laser Guide Stars for the Keck Telescopes", C. E. Max, D. T. Gavel, S. S. Olivier, J. M. Brase, H. W. Friedman, K. Avicola, J. T. Salmon, A. D. Gleckler, T. S. Mast, J. E. Nelson, P. L. Wizinowich, and G. A. Chanan, 1994, Proc. SPIE 2201, p. 189.
  2. "Limitations and Expected Performance of Adaptive Optics at Keck", C. E. Max, D. T. Gavel, S. S. Olivier, and J. Brase, 1995, Adaptive Optics for the Keck Observatory (book), chapter four, W. M. Keck Observatory Report 208, 146 pages.
  3. "Performance predictions for the Keck telescope adaptive optics system", D. T. Gavel and S. S. Olivier, 1995, Proc. SPIE 2534, p. 401.
  4. "Near Infra-Red Astronomy with Adaptive Optics and Laser Guide Stars at the Keck Observatory", C. E. Max, D. T. Gavel and S. S. Olivier, 1995, Proc. SPIE 2534, p. 412.
Laser History