title: Focus anisoplanatism: a limit to the determination of tip-tilt with laser guide stars.
abstract: One limitation to using laser beacons to measure tilt is focus anisoplanatism. By use of a spectral representation for the atmospheric turbulence, the wave-front error is expressible as an integral over the distribution of turbulence with height. Results are calculated for turbulence profiles typical of astronomical sites. The decrease in Strehl ratio when a single laser guide star is used to measure tip-tilt is shown to be especially significant at visible wavelengths, precisely where tip-tilt is most difficult to obtain from natural stars.
authors.forename: C R
authors.initials: CR
authors.lastname: Neyman