Image improvement from a sodium-layer laser guide star adaptive optics system

Science

Volumn 277, Issue 5332, 1997, Pages 1649-1652

  Max, C E ^a   Olivier, S S ^a   Friedman, H W ^a   An, J ^a   Avicola, K ^a   Beeman, B V ^a   Bissinger, H D ^a   Brase, J M ^a   Erbert, G V ^a   Gavel, D T ^a   Kanz, K ^a   Liu, M C ^b   Macintosh, B ^a   Neeb, K P ^a   Patience, J ^c   Waltjen, K E ^a  

^a LAWRENCE LIVERMORE NATIONAL LABORATORY   (United States)

^b UNIVERSITY OF CALIFORNIA   (United States)

^c UNIVERSITY OF CALIFORNIA   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

ARTICLE; ASTRONOMY; IMAGING SYSTEM; OPTICS; PRIORITY JOURNAL; REFRACTION INDEX;

EID: 15444345743     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: 10.1126/science.277.5332.1649     Document Type: Article

References (27)

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13. M. Lloyd-Hart et al., Astrophys. J. 439, 455 (1995). This system allowed control of relative tip-tilt between two (and, subsequently, all six) of the Multiple Mirror Telescope's 1.8-m primary mirrors.
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15. A Shack-Hartmann sensor divides the telescope pupil into subapertures with the use of a set of miniature lenses (lenslet array) placed in a reimaged pupil plane. The average wave front slope in each subaperture was determined by measuring the position of the focused image formed by each lenslet. The constraint of continuity could then be imposed, and an estimate of the wave front phase could be reconstructed, for example, from a leastsquares fit.
16. Because the laser travels up through the turbulent atmosphere before forming the guide star, the instantaneous physical position of the guide star is variable. This upgoing beam wander results in a difference between the apparent instantaneous positions of a laser guide star and a natural star, rendering the laser guide star unsuitable as a reference for stabilization of the overall image position of astronomical objects. The solution is to use a faint natural star as overall tip-tilt reference. If this technique is used, the sky coverage for a laser guide star adaptive optics system is limited by the availability of suitable tip-tilt reference stars [S. S. Olivier, C. E. Max, D. Gavel, J. Brase, Astrophys. J. 407, 428 (1993); (14)]. Because the requirements for a tip-tilt reference star are less severe than those for a high-order wave front reference beacon, the use of a laser guide star increases the sky coverage fraction for adaptive optics systems.
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21. 2 (assuming that they have roughly the same spectrum as the tilt-corrected atmosphere), the expected intensity increase was only a factor of 1.7. The measured value was 1.4. The degraded tip-tilt performance was attributable to misalignment of the tip-tilt sensor and nonoptimal tuning of the tip-tilt control parameters.
22. 2 (assuming that they have roughly the same spectrum as the tilt-corrected atmosphere), the expected intensity increase was only a factor of 1.7. The measured value was 1.4. The degraded tip-tilt performance was attributable to misalignment of the tip-tilt sensor and nonoptimal tuning of the tip-tilt control parameters.
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25. 1/2, where κ is the ratio of the sampling frequency to the control bandwidth (13).
26. o = 3 to 5 arc sec is the isoplanatic angle. Hence, finite laser spot size was not a significant factor in our data.
27. This work was performed under the auspices of the U.S. Department of Energy by the LLNL under contract number W 7405-Eng-48.