The use of laser guide stars in astronomy

Details The use of laser guide stars in astronomy The use of laser guide stars in astronomy

Aug 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002phdt.........8n&link_type=abstract

Thesis (PhD). UNIVERSITY OF ILLINOIS AT URBANA-CHAMPAIGN, Source DAI-B 63/02, p. 861, Aug 2002, 102 pages.

Physics

Optics

3

Scientific paper

This thesis discusses and tests the use of laser guide stars as references with adaptive optics systems. The two major deficiencies of laser guide stars are (1)their limited ability to track an astronomical source, i.e., measure the overall tilt on the incoming wavefront; and (2)their inability to sample the atmospheric turbulence at high altitudes, a deficiency know as focus anisoplanatism or cone effect. In the first section of this thesis analytical results are presented for the error when a laser guide is used to sense tip-tilt in methods proposed by various authors. The results presented in this thesis show that the use of a Na laser guide star for tilt sensing is feasible only on a 4-m diameter telescope in the visible or on a larger 8-m telescopes only at near infrared wavelengths. The second part of thesis deals with the ways multiple laser guide stars can be used to reduce the cone effect. Computer simulations of multiple laser guide star systems show that multiple LGS can reduce the error from cone effect to acceptable levels. However, the relative wander in the positions of the laser beacons in a multiple guide star system ultimately limits the accuracy of these systems. In addition to simulations of the error from guide star wander, experiments were conducted with an excimer laser producing Rayleigh guide stars at an altitude of 10 km on a 1-m telescope. This experimental system was successfully used to photometrically calibrate the expected return from a single laser guide star. Furthermore, measurements of beacon wander from two laser guide stars showed the utility of the full aperture broadcast of the laser beams as one method to reduce beacon wander in a complete multi LGS adaptive optic system. This experiment and the simulations were in approximate agreement if a strong turbulent layer is added to the Mt. Laguna turbulence profile at an altitude of 3.6 km mean sea level.

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